On a cloudy day in Derry, Maine, a little girl is riding her tricycle down the street. Her mother, seeing a storm approaching, calls for her to come inside as she brings in the laundry. The little girl then spots a clown behind the laundry. A moment later, her mother comes outside to bring in the rest of the laundry, and screams: the little girl is dead. Shortly afterward, as the rain falls, the town librarian, Mike Hanlon, comes looking around and talks to the police, much to the chagrin of the police chief, who is frustrated. Before he leaves, Mike spots an old photograph of a boy, which he's seen before, laying on the ground. Later, writing in his journal, he notes the murder as "another killing", and how he found the photograph, and is at a loss to explain how it suddenly turned up after 30 years. He decides that he has to call his old friends up, hoping that he is mistaken. He picks up the phone and starts dialing (presumably he has been keeping track as the years passed.)
Mike's first call is to England, where Bill Denbrough is working on turning one of his horror novels into a movie, even as his dinner gets cold. His wife Audra is unhappy that he spends so much time working. The phone rings and Mike identifies himself. Bill has a flashback to when he was talking to his friends as a boy; this was the first time he thought of them or Mike in years. Mike tells him "It's back", and about how he found the photograph. Bill, who had barely touched his dinner, goes off back to his work room, where he has a longer flashback.
In Bill's flashback, his mother is playing the piano one rainy afternoon while Bill lays in bed, recovering from an illness. His younger brother George (the boy in the photograph) is bugging him to talk to him or play with him. Bill doesn't feel up to it, but he gives him a paper boat to play with. Bill seals it with wax while George puts on his rain gear. George goes out to play, and that's the last time Bill sees him. George sails his paper boat down the gutter, which is full of rainwater. Unfortunately, the boat is swept into a storm drain. George is upset at losing the boat, and is ready to leave when he spots a clown in the drain. George is nervous at first - his father warned him against interacting with strangers - but the clown introduces himself as Pennywise, and already knows George's name, which means George "knows" him. Pennywise holds out the boat to George, but when George reaches for it, Pennywise grabs his arm instead. George screams. The next scene is George's funeral. Later, Bill, still in shock over his brother's sudden death, goes into George's old bedroom and looks at George's photo album, and finds the picture of George that Mike would find decades later. Suddenly the picture winks at him. Bill is horrified and throws the album on the ground. Blood begins to seep from it. Bill screams in horror, and his parents come in. They simply put the album back on the shelf. They can't see the blood, and demand that he never enter the room again.
Coming out of his flashback, Bill wonders how he could have forgotten, and he prepares to leave immediately. He tells Audra about the phone call from Mike, and how he has to return to his hometown. He has also begun to stutter, which he did when he was a kid. Bill leaves, leaving Audra on edge.
The next scene is in New York, where a drunk bearded man steps out of a limousine, bringing a foreign woman home with him (apparently one he just picked up, as she hasn't seen his place before.) A picture of the man on the cover of Time Magazine identifies him as Ben Hanscom, an architect. Just then the phone rings. It's Mike. Ben has a short flashback of his own, to when he was being confronted by bullies as a kid. Ben is very shaken. Mike tells him that "it's back". Ben doesn't remember much, but tells Mike he'll come home. Very rattled, he pours himself another drink, leaving the woman behind he goes up the elevator to the top of one of his half-finished buildings, contemplating suicide. There he too has a longer flashback.
Ben remembers introducing himself as a new student in Derry, where he has just moved with his mother to live with his aunt. The bullies of the class dislike him on sight because he is fat. Their teacher reminds them about the curfew, imposed by the sheriff because of all the killings that have been going on. He meets a girl from the class, Beverly, and immediately likes her. Walking down the street, he is confronted by the bullies he met earlier. These are Henry and his friends. Henry confronts Ben with a switchblade, disturbing even his own friends. Ben kicks Henry in the nuts and pushes himself back, through a fence and down an embankment into a wild area. The enraged Henry and his friends chase him. Ben spots a drain pipe to hide in. Henry doesn't find him, but he finds two other boys playing in the stream. They push them around and ask them if they'd seen Ben. They hadn't. Henry and his friends leave, disgusted that Ben was able to ditch them. Ben comes back out and meets the other two boys, one of whom, Eddie, is having an asthma attack. The other - the young Bill - has to go and get medicine. Ben and Eddie talk about how they both lost their fathers - Ben's in the Korean War, Eddie's to cancer - Eddie tells Ben about how Bill's brother had been killed a little while back. Bill and Eddie tell Ben about how they were trying to make a dam in the stream, and Ben comes up with an idea for an improvement. They invite him back the next day. Later, Ben is writing a postcard, intended for Beverly, when his cousin (with whom he is now living) comes in and reads it, taunting him. The embarrassed Ben wrestles him. The cousin is clearly unhappy about having Ben around, reminding him that he's only their because his mother (Ben's aunt) felt obliged to take Ben's mother in to keep them off the welfare rolls. Ben's aunt reminds Ben's mother of this, too. Ben, who doesn't want to be there either, goes for a bike ride. He finds himself back in the wooded area, and there he thinks he sees his father. His father talks to him, but gradually his voice and appearance change, until he has turned into the clown. The clown vanishes suddenly, and a skeleton climbs out of the water. Ben is horrified and retreats. Ending the flashback, the adult Ben remembers these horrors and drops his bottle 16 stories to the street below.
Next up is Chicago, where Beverly Marsh is now a fashion designer. Mike's call comes in, but her boyfriend Tom Rogan rebuffs the call and reminds Beverly about an upcoming deal with Japanese investors. The two of them go out into their factory to meet the investors. Later, Beverly and Tom drink up the champagne. Apparently the deal went through. The phone rings again, this time Beverly gets it. Mike was persistent, and tells her the news. Tom, who went to the refrigerator to get more booze, returns to find Beverly packing. He is immediately angered and starts beating Beverly, getting out his belt. For the first time, Beverly stands up to her abusive boyfriend, throwing jars at him and hitting him in the forehead. This stuns Tom for a moment, long enough for her to escape. She gets in a cab to go to the airport. During the ride, she has a flashback of her own.
She remembers being a girl and making breakfast for her father, when the doorbell buzzes. It was Ben, but he doesn't stay there to greet her. He simply left the postcard on the porch while he crouched down across the street to make sure she got it. Beverly's father sees the postcard and immediately confronts her about it, thinking she's running around with boys already even though she's only 11. Her father starts smacking her around (this treatment obviously influenced her as an adult, as she ended up with Tom). Beverly runs out of the house and down the street. Her father stands on the porch and shouts after her, but does not give chase. Concerned that he might have caused this problem, Ben goes off to find her, and finds her crouching behind a bush. Ben invites her to come with him to the wooded area where he was going to build the dam with Bill and Eddie. They are about to start when they are approached by two more boys, Richie Tozier and Stan Uris, who are also friends. Richie is a wise-ass, and Stan is quiet and intelligent, a Boy Scout. The six of them work for several hours on building the dam out of rocks, dirt, and garbage, and it is a success, they end up with a pretty big pool. At the end of the day, Bill, Ben, and Beverly take leave of one another. Beverly starts to think Bill wrote the postcard; she likes him. Ben sees this, much to his dismay, but says nothing. Beverly goes home where her father is watching TV, apparently having forgotten about the morning's events or not in the mood to talk about it. Beverly goes into the bathroom to wash up and hears voices coming out of the drain in the sink. Suddenly blood bursts out of the drain. Beverly screams and gets her father to come look, but he can't see any of the blood. He thinks Beverly freaked out for no reason. Beverly makes up a story about a spider that scared her to satisfy her father. As soon as he leaves, the voices start again, and Beverly is terrified. She remembers this as her cab arrives at O'Hare.
Next up is Eddie, now leaving on Long Island. He has just gotten Mike's call and is preparing to leave by filling his bag with pills and medicine. He still lives with his overprotective, smothering mother, who demands to know where he is going, and is unhappy when he says Derry. He leaves with his driver - he now runs a limousine company. The driver is worried about him, but takes him to Penn Station. While they are driving, Eddie has his flashback.
Eddie remembers being in a theater watching "I Was a Teenage Werewolf" with his five friends, Richie, Stan, Ben, Beverly, and Bill. He accidentally kicks a bucket of popcorn over the railing, where it lands on Henry and his friends. Richie decides to instigate further, insulting Henry and pouring his Coke on them. The six decide they'd better get out while they can, and run from the theater, reaching the wooded area. They pass by the swamp and the sewer building where Ben saw his father's ghost earlier. Returning to civilization, they arrive at Eddie's house. His mother immediately comes out and chases the others away, telling them that Eddie needed to rest and that he didn't need any friends except his own mother. She reminds him not to take a shower at gym class because of germs. On his next gym class, the coach notices, and instructs him to go take a shower. All the other boys have left, so he has the shower to himself. Suddenly all the showers in the room come on by themselves, and then the shower heads themselves lengthen and reach out from the wall, spraying Eddie with water. Then the clown's voice comes out of the drain. It then pushes the sides of the drain apart with its hands and sticks its head out. Eddie retreats, wheezing with his asthma as the clown talks to him. He escapes, remembering his fear as he gets on the train heading for Boston.
Mike's next phone call goes to Beverly Hills, California. There, Richie Tozier has become a comedian, just finishing his routine. He leaves the stage, talking to his assistants. It's pandemonium in the back rooms. Richie finally picks up the phone. It's Mike. Richie immediately gets ready to leave for Derry, angering his manager, who thinks Richie is just running away from several important comedy jobs for a trivial reason. He has his own short flashback, being attacked by a werewolf in a cellar. Then he goes to the toilet to vomit and remembers the rest of that day.
In that flashback, Richie remembers listening to Bill telling a story, which all of his friends enjoy immensely. They sit around their campfire, built next to the dam they built earlier, talking about what they might want to do when they are grown. Bill, suddenly quiet and serious, starts to tell them something very important, warning them not to laugh or make fun. He is about to tell them the story of how George's photograph winked at him when they are interrupted by Officer Nell, who has come down to see why the storm drains aren't draining properly. It was the dam the kids built. They all own up to having worked on the dam. The policeman tells them to tear it down, reminding them to always play as a group because of the killer on the loose; another child was killed that morning. The next day at school, Stan and Richie are confronted by Henry and his friends in the cafeteria at lunchtime. Henry is still angry about having cola poured on him at the theater, and rubs mashed potatoes on Richie's glasses. Richie, tired of being pushed around and ever the smart-ass, throws his lunch in Henry's face and runs. Henry chases him but slips in some food and falls. Richie taunts him and takes off to run again, but this time collides with the school principal, spilling the principal's lunch all over the principal. Henry, knowing enough to not press the issue any further that day, stalks away. The school principal tells Richie to go get a mop from the janitor (who happens to be Beverly's father) to clean up the mess. Richie goes into the cellar to look for him, but instead finds the werewolf that he saw in the movie. The werewolf catches him, but Richie is able to wiggle free. When he looks back, the werewolf has turned into the clown. Richie runs away, back into the cafeteria. He says there's a werewolf in the cellar, and everyone laughs at him except his own circle of friends. Richie remembers being scared even as he tried to sleep that night as we shift back to the present.
The next story is Mike's own. He looks at an old photograph and writes in his journal, remembering how he entered that particular circle of friends. On show-and-tell day at school, he brought an old photo album that his father assembled with pictures of Derry's past. He talks about the disasters in Derry's past, an explosion at the ironworks in 1930, some drowning deaths in 1900. The teacher is somewhat upset by the morbidity. Later, on the street, Mike is confronted by Henry and his friends. They intend to put a firecracker in his pocket. A businessman across the street shouts at Henry, giving Mike just enough time to grab his photo album and run. Henry and his friends chase him. Meanwhile, in the wooded area, the six friends are talking about what they've seen. All of them are relieved that they weren't the only ones to see something, except Stan, who hasn't seen anything yet and doesn't believe any of the stories. They are still talking about it when the winded Mike comes over the ridge, having run all the way from town with Henry and his friends close on his heels. Bill decides they should take a stand where they are at, and begin to gather rocks to drive off Henry. Mike reaches where the others are standing just before Henry and his friends arrive. He recognizes all of them, and hates all of them, and insults all of them, calling them the "Losers' Club", but tells them he only wants Mike that day. Bill's circle begins to throw rocks, and several of them start fistfights. One by one, Henry's friends retreat, until only Henry is left. Outnumbered 7 to 1, Henry also retreats, promising to kill the other kids. The others welcome Mike to their Losers' Club. Mike takes a photograph of all of them, the same photograph he would look at 30 years later. Then he shows the others the rest of his photographs and engravings. Even in the 1700s, there were pictures of Pennywise the Clown. The album begins to move by itself, until it opens to a picture of a street with a horse-drawn carriage. Suddenly the picture begins to move, the horse and people move around, and then the clown comes running down the street. It climbs up onto a light pole in the foreground and talks to the Losers out of the photograph, taunting and threatening them. The horrified kids close the book and reopen it, where the photograph is the same as it was before the movement started. Stan witnessed it too, he was the last one. He just wants to forget about it. The kids decide they'd better try to do something about it. Bill, who lost his brother to the monster, asks the rest of them to help him kill the monster.
Mike remembers all this writing at the library after hours. When he looks up, there are muddy footprints and a balloon on his desk.
Mike then places his last call, to Stan Uris, now living in Atlanta. Stan hesitates when Mike reminds him of his promise and asks him to come. Stan returns to the living room where his wife asks who was on the phone. Stan, looking rattled, goes up to take a bath, which is out of character for him at this time of the evening. As he gets undressed, he has his flashback.
He remembers reciting the Boy Scout Oath. The seven Losers are having a slingshot competition, to determine who should be the one to shoot at the monster. Beverly is far and away the best shot, getting 10 out of 10 shots. No one else did better than 3. Richie gives Beverly two silver earrings that he sneaked from his mother's jewelry box, this will be their ammunition against the monster. Stan remains skeptical as they walk toward the sewer building on another rainy day. They all take a shot from Eddie's aspirator - something to unite them - although Richie remarks that it's disgusting and tastes like battery acid. Then they enter the building. Henry and his two closest friends were just outside, and follow them - Henry intends to make good on his promise that he made on the day of the rock fight. The Losers' Club, still unaware of Henry, descend into the sewers. Henry sees them and sends his friends into other pipes, hoping to trap the Losers. They know the layout of the pipes because they chased a dog through the sewers one time. The Losers walk through the pipes, with Eddie, the best navigator, directing them. Suddenly the monster appears, in the form of a bright white light, and attacks Victor, Henry's friend that he sent off to chase the Losers from another direction. Belch (Henry's other friend) and Henry capture Stan silently even without Victor's help and drag him away. The Losers don't immediately notice his disappearance. Henry and Belch are preparing to torture and kill Stan when the monster comes for them, too, again in the form of white light. The monster takes Belch first, and then comes back, although it does not take Henry, his hair turns white immediately from fear and shock while Stan runs off. Stan catches up with the rest of his own group, just ahead of the monster, which soars over them. As they glance up, they see a large, glowing light grid, shaped almost like a turtle shell. The monster passes them by. The kids are still alive and unhurt, clearly the monster was not as strong as it would have liked. A fog suddenly comes out of the walls, forcing the kids to grab hands to stay together. Apparitions appear to several of them, trying to get them to break the circle. The clown appears and grabs Stan. The clown tells the group that it deliberately frightens the children before killing them because they taste better when they are scared. Eddie distracts the clown with his aspirator, remembering Richie's remark about battery acid, long enough for Beverly to shoot it with the first silver earring. The clown jumps into the drain to escape. The kids try to grab it to prevent it from leaving, but its claws break through the clown gloves and eventually, a large, 3-fingered claw takes the place of the clown's hand. The kids scream and the monster escapes. It growls in agony, leaving the kids wondering whether or not they really killed it. Still uncertain, they leave, and Bill asks them to swear to him that they will all come back to fight it again if it ever shows up. Again, Stan hesitates, and he ends up being the last one to swear.
Back in the present, Stan's wife comes to the bathroom, puzzled by the extended silence. She enters the bathroom and sees Stan in the tub, dead. He committed suicide by slitting his wrists. He drew the word "IT" on the wall in his own blood. His wife screams, and thus ends the first half of the movie.
The second half of the movie begins with Bill arriving back in Derry for the first time since he was a kid. The woman at the motel is starstruck, she is a fan of his horror books. Feeling restless, he goes for a cab ride, seeing how downtown has changed. The movie theater is now abandoned. Bill arrives at the cemetery where George is buried and visits his graves. Then he has a vision of Pennywise in front of seven graves, one of which appears to be taken already. When he looks again, there is nothing there. He then goes to the city library where Mike works. Some of his own books are on display. He sees Mike for the first time in years. Mike welcomes him and they go for a walk. Bill doesn't remember much - yet. They arrive at Mike's house, who lives just down the street from where Beverly lived as a girl. They have a beer, and then Mike shows Bill a surprise. He found Bill's old bicycle in a pawn shop a year earlier, and bought it, just in case. Bill fixes up the bike while Mike changes clothes. Putting his hand on the handlebar, Bill has another flashback, this time of helping Stan escape something on the bicycle.
Richie arrives in a rented car and gets a scare of his own, seeing his own obituary on the marquee outside the abandoned theater. He races to the library to find Mike, but Mike left with Bill a little while earlier. Richie decides to wait for him. He is very much on edge and jumpy. Then he hears the clown's voice. No one else hears it, and when he replies to him, everyone looks at him funny for talking in the library. The clown appears and sends down many blood-filled balloons, no one else notices. The clown continues mocking Richie while he talks to the assistant librarian, more and more hysterically. Richie flees the library.
When Mike comes back into his back yard, Bill has got the bicycle in rideable condition. They go for a bike ride together for old-time's sake, remembering how they did much the same thing as kids. Mike hands Bill a deck of cards to stick in the spokes for noise. Bill fumbles the deck and drops the cards, and the two of them receive three scares at once: Only two of the 52 cards land face up. Both are the ace of spades. And the back of the cards has the picture of the clown on them.
Ben arrives in town in a cab, and tells the driver to stop and wait for him at the bridge over the stream that he helped dam up many years before. He goes down to look around and sees a fat boy climbing down the embankment with some other boys close behind. He immediately remembers when he did the exact same thing, fleeing Henry, 30 years earlier. The bullies push the fat kid to the ground and run away. Ben, sympathizing with the fat kid, ties his handkerchief around the kid's injured leg. Then Ben goes toward the swamp where he saw his father's ghost. This time, he just sees a skeleton, and then nothing. A hand falls on his shoulder, and the jumpy Ben almost screams, but it was only a bum asking for spare change. A shaken Ben gets back in the cab and they continue into town. Ben sees the clown by the roadside.
Eddie also arrives downtown, and his first stop is the drugstore where he got so much of his asthma medicine in the past. He has a flashback to when he was 11. The drugstore's proprietor, thinking he is now old enough to understand, takes him into the back and tells him that so many of his problems are all in his head. His mother stifled him so much and convinced him that he was always sick, and Eddie doesn't believe it when the drugstore's proprietor tells him that his medicine is only a placebo. The adult Eddie still needs the stuff, and picks up some at the drugstore. Then he sees the proprietor in the back. His grandson runs the store now, the old man has retired and doesn't seem to be quite all there any more. But he does remember Eddie, saying a few disjointed words about the placebo. Suddenly the old man grabs Eddie's arm and the clown's voice comes out, warning him to leave town. As quickly as it started, he goes back to being a senile old man.
Beverly arrives on foot at her old house, hoping to meet her father. Instead a woman in late middle age answers the door, informing Beverly that her father has been dead for five years. The woman invites Beverly inside for tea. Beverly goes to the bathroom, and stares into the sink where the blood came out years before, before washing up. Instead of blood coming out of the sink, it rapidly fills with droplets from the tap. She comes back into the main room, admiring what the woman had done to fix up the house. But the woman's appearance gradually changes, becoming uglier. Beverly's tea cup suddenly contains blood. The woman's voice changes to her father's voice, and Beverly runs out into the street. She looks back and the clown is on the porch. A truck almost hits her in the street, and when she looks back again, the house is abandoned and boarded up.
Back in England, the movie producer has come to see Audra, enraged by Bill's sudden departure. The producer swears that Bill will never work on another movie, and warns Audra not to leave too lest her career meet the same fate. Audra, worried about Bill, leaves anyways. Mike has arranged a reunion dinner at a local Chinese restaurant in Derry. One by one, the Losers arrive, marveling at how they have changed, Ben having lost weight. Richie is the most shaken, going to the bathroom to regain his composure before he goes back to greet them and be a smart-ass. Beverly is the last to arrive, even fainting from the stress. When she comes around, they share stories of what they saw during the day. All of them got scares of some kind. None of them remember very much yet. At Richie's request, they decide to go ahead with the dinner even though Stan has not yet arrived (they do not yet know that he is dead) and talk about something other than the monster for awhile. They do so.
They have a big meal and talk about several subjects. Richie's multiple failed marriages, Ben having escaped it several times. Eddie says he's seeing someone but doesn't have much spare time. Beverly mentions her boyfriend. Then the topic turns to Henry. It seems Henry was blamed for all the killings in 1960, had confessed, and he had been sent to an insane asylum where he remained to this day. That same day, the clown appeared in the moon and started talking to Henry. The clown wants Henry to break out of the asylum and go back to Derry and kill the Losers.
At the end of the meal, Richie announces his intentions to leave the next morning. He's clearly not committed to killing the monster. Eddie isn't enthusiastic, either, but they realize they're all beating around the bush and not talking about the monster. The group opens their fortune cookies and they get scares from them. All of them contain something disgusting - an eye, a baby bird, something with claws, a gout of blood, a cockroach, and a spider. The Losers flee the restaurant and go to the library.
There, Mike tries once more to call Stan. Beverly sees the blood from when Richie got his scare and remembers trying to clean up the blood in her bathroom when she was little. As soon as she had cleaned it up, more blood came out. Richie begins to tell jokes, trying to lighten the mood. Mike hangs up the phone, having just learned that Stan committed suicide. He informs the group. The suddenly somber Losers begin to talk about the monster. Suddenly Bill understands why he saw one occupied grave out of seven in his vision at the cemetery earlier that day. Then he remembers a day when they were kids when Stan had almost been killed, even after the day he saw the moving photograph with Mike and the others. Stan had been birdwatching at the park when some voices called to him from a nearby house. He went to investigate, figuring there was a rational explanation, and when he entered, the door closed and locked behind him, and a mummy began to walk down the stairs toward him. Stan, unable to think clearly, simply started to recite the names of all the birds he could think of. It worked, the mummy withdrew and the door opened. Stan escaped and ran away through the park. Eddie remembers that Stan had also seen the monster when it had taken Belch and driven Henry insane, seeing not the clown but what was behind the clown, which he referred to as "the deadlights". Mike opens the refigerator and dozens of balloons sail out, leaving Stan's head inside. The head taunts the suriviving Losers before Mike slams the door closed. All the doors in the library slam shut and books fly off the shelves, Papers fly around randomly and the typewriter types with no one operating it. Rain begins to fall indoors. The six of them gather together and form a new circle. The rain stops and the lights come back on. Bill looks at the paper in the typewriter. His stutter is getting worse and he can't read it aloud. Ben does it for him: "He thrusts his fists against the posts and still insists he sees the ghosts". It's an exercise to help stutterers. They leave, carrying boxes of supplies with them.
At the insane asylum, the moon sets and Belch appears under Henry's bed. Henry speaks aloud, attracting the attention of the ill-tempered night guard. Belch tells him to just think what he wants to say. Belch, invisible and inaudible, tells Henry that he will need to get out, because Henry was a living, mortal human being, and could not be stopped by silver or incantations. Belch tells Henry to walk toward the door, and he would take care of the guard. Sure enough, when the guard comes out to beat up Henry, Belch appears to him as Doberman Pinscher wearing a clown suit, allowing Henry to escape.
At the hotel, the Losers continue their discussion. Richie, seeing flashlights and helmets in the boxes, drunkenly shouts that he does not want to go into the sewers. Eddie asks Mike to tell them more stories about the monster. Mike hands around old newspapers and tells them about all the children who were killed or disappeared. No one did anything except they themselves, and when Henry confessed the killings stopped. He tells them about the disasters that happened in town every 30 years. They remember his show-and-tell presentation, and Beverly notices for the first time their teacher deliberately didn't want to know. She also remembers how Henry and his friends had sexually harassed her outside her house one day, and she looked across at a neighbor hoping for help, but the neighbor simply went indoors. Only the arrival of her father saved her, one of the few times she was happy to see him. Mike told them about the killings that had started in the present, and then showed them the picture of George, which he had found at the latest crime scene only the day before.
Mike then notes how their being together and united made them strong, and protected them from being picked off one by one. Then he notes that all of them who left, including Stan, had become at least moderately rich. Mike had stayed put and was still lower middle class at best. Also, none of them had had children. Even in the era of birth control, seven people childless at age 40 was quite a coincidence. Meanwhile, Audra arrived in town at night and was immediately confronted and taken, although not killed, by the clown, who posed at first as a gas station attendant.
Ben told the story of how he had gotten thin. In high school, he had been inspired by a cruel gym coach to start running and try out for the track team. After some months, he kept his word and beat the coach's best guys at track and asked the coach to apologize. The coach hit him instead, and lost his job. But they are once again beating around the bush. Beverly tells them about how when all of them came to help her clean up the blood in the bathroom, it never returned. As the night wears on, they decide to return to their rooms to take a break and refresh themselves. It's not a good idea to separate, so they keep their doors open. Nevertheless, Mike is attacked by Henry in one of the rooms while he's by himself. Beverly finds Ben and asks him about the postcard and Ben admits to it and kisses her, only for her to change into the clown again - Beverly was never really there at all. The clown disappears. Eddie finally hears the commotion, and he and Ben break into the room where Mike and Henry are. Henry, who now looks like an old man, managed to gravely injure Mike, but he ended up impaled on his own switchblade and died. The Losers load Mike into Richie's rented car and go to the hospital. In the morning, they wait around while the doctors examine Mike. Beverly talks to Ben about the monster. Then she tells Ben she now sees the mistake she made, getting together with Tom, who turned out to be abusive, everything she hated in her father. Ben tries to console her, telling her that he had never really felt anything and she was luckier in that regard. Beverly mentions the postcard, and Ben, remembering his last encounter with Pennywise, is shocked, but this is the real Beverly, not the clown; and they begin to kiss. Just then, Eddie comes outside to get their attention. Mike will live, although he isn't going home any time soon. Bill goes to see him and they come up with their cover story in case anyone asks about the accident. Mike directs Bill to his jacket. In the pocket are the silver earrings. Mike tells Bill how some few years ago, he was feeling depressed and close to suicide. He went back into the sewers to look for the earrings, halfway hoping the monster would wake up and kill him. When he came out, he got things together, but the fear had made him start to turn gray. Back at the hotel, the five remaining Losers cover Henry's body and decide not to involve the police yet. They think something would happen to them if they did. Richie and Eddie are ready to leave town, but Ben persuades them to hang a Do Not Disturb sign on the door to buy time while they went outside to talk further. They leave the hotel. Bill is the last one, and before he leaves, he sees a woman and her son playing the piano in a room off to the side. They were playing the same piece his mother was playing on the day George died. Bill comes back outside, where the others are all ready to leave. He tells them he can't leave. He has made a living scaring people, but he has been scared his whole life by what had happened. After the fun times at the reunion had worn off, it is revealed that all the Losers, although well-off, have been unhappy and screwed-up as adults. Bill doesn't want to be scared any more. He vows to return to the sewers to kill the monster, and once more asks them to come back with him to kill the monster. One by one, they come over to him, Richie last.
In Richie's rented car, they return to the bridge over the stream. Beverly still has the slingshot, the only thing she saved from the old days. Bill gives her the earrings, telling her about Mike, and saying the earrings were for Mike and Stan. Richie is still unhappy about going through with it and states that they should've brought a gun instead, but he comes along. They enter the sewer building and climb into the same pipe they went into thirty years earlier. The first thing they see, instead of an orange pom-pom like the last time, is a purse - Audra's purse. Bill, for the first time realizing that she followed him, runs through the pipes calling for her. The others hurry after him. Bill blames himself for telling her where he was going..They remind him that they must kill the monster to save her.
They continue through the pipes, Eddie navigating as before. They arrive in the four-way chamber where they had their showdown the first time. The building has been neglected. The cracks in the walls caused by the first confrontation with the monster thirty years earlier were never repaired, and plant roots have come through the walls and ceiling. Just then, the paper boat appears after a 30-year absence. George's ghost appears to Bill and blames him for his death. The others remind him that there's nothing really there, and that Bill was not at fault for George's death. The ghost vanishes. Bill challenges the monster to show itself. The clown appears to them, still taunting them, and vanishes. Richie thinks it's impossible to fight a ghost that vanishes, but Bill reminds them, the monster eats, and in order to eat, it has to take a physical form which can be killed. He places the paper boat in the water channel and follows it as the currents carry it away toward the monster.
The channel goes into a tunnel and continues through a cave that appears not to be part of the sewer at all. There are human bones scattered around the cave, and a small door surrounded by candles leading to the monster's lair. Before they go through the door, Eddie confesses that he lied earlier. He isn't seeing anyone, and he never has. He's still a virgin, even though he's 40 now.
The group goes through the door, into a large, alien cave. There are bodies suspended from the ceiling in things that look like cobwebs. One of them is Audra, who appears to be in a vegetative state. Finally the monster appears to them, in the form of a giant spider. The spider has razor-sharp teeth and the same 3-fingered claws that the Losers saw the first time they defeated the clown. Beverly shoots at the spider, but the silver slug bounces harmlessly off the spider's exoskeleton. Beverly shoots again, with the same result.
The spider then stands up and light glows from his chest, hypnotizing Bill (the light appears to be coming from the same glowing grid that passed over the group in the sewers during their first confrontation). Ben and Richie approach and are also hypnotized. Only Eddie and Beverly are left. Beverly goes around the spider to look for the silver, while Eddie remembers Richie's remark about battery acid. Shielding his eyes from the hypnotizing light, he steps forward and shoots his aspirator at the spider, saying it's battery acid. The spider is unfazed, picking up Eddie. Beverly finds one of the slugs and shoots the spider in the chest. This part of the spider is vulnerable, and it collapses, dropping Eddie, who was mortally wounded. He dies surrounded by his friends.
The spider crawls off, moaning, deeper into the cave. The remaining four Losers have gained in resolve. Even Richie is committed to finishing it off now, and they pursue it. They corner it, push it over on its side and punch into its still-glowing chest, finally tearing out its heart and hoisting it overhead. The monster is dead at last.
Bill, remembering Audra, returns to the room he just left, where the cobwebs are rapidly decaying, lowering the bodies to the floor. Bill catches the catatonic Audra and carries her. They return to the outside world, with Richie carrying Eddie's corpse.
Mike, some few weeks later, read his journal entry about the adventure, having started to forget things himself. He will be out of the hospital soon. Richie had returned to Los Angeles and had a part in a comedy movie, with another comedian who look and acted like Eddie. Ben and Beverly left together. Before long they had gotten married, and shortly after Beverly was pregnant. Another curse was broken. Bill and Audra were still in town, but Audra's condition was unchanged. Just before they were set to go back home, Bill spots his old bicycle by Mike's house. He climbs onto it and puts Audra on his lap and starts cycling down the hill toward downtown. The trick worked, Audra wakes up, although she has no idea where she is, all is well once again.