It is about March of 1968. A young lady in her early twenties and her husband pull up in their 1969 Ford Country Squire Station wagon to a lavish upstate New York home on a lake, near the town of Ilium, believed to be the fictional title for the actual city of Schenectady. She frantically knocks on the front door calling for her father and no response. She peers through all the windows of the lavish home and sees nothing. Then she lets herself in the back of the home in the utility room desperately searching for her father.
In the basement of his home, Billy Pilgrim, a balding, bespectacled, mild-mannered, and passive man of 45 years of age is typing a letter to his local daily newspaper of his time travels and how he is uncontrollably traveling from one point of his life to the other, being "unstuck in time". While he is typing his letter, he finds himself at the Battle of the Bulge in Belgium in January 1945, at the age of 22 alone and running through the snow. He is not dressed as a soldier at all, no weapon, and wearing a stocking cap, overcoat, sweater, and pants that are nothing suggesting Army attire. He is kidnapped by two brash, uncouth, mean, and very stupid men of his age, fellow soldiers named Paul Lazzaro and Roland Weary. They immediately think he's a German, but he denies it and they soon forget about it, since there's an attack going on. The men's Corporal abandons them and Lazzaro swears revenge.
Briefly, Billy finds himself back on planet Tralfamadore in the geodesic dome with beautiful, 20-something porn star queen, Montana Wildhack and she suspects he's time traveling again and wants to give him a kiss to help forget about it. Simultaneously, Billy is back at the Battle of the Bulge and Paul Lazzaro hears him say "a little kiss" and Lazzaro is outraged beyond rationalization and accuses Billy of being homosexual, violently attacking him. Shortly after, two German guards take them at gunpoint tell them to get up and for Weary to give up his boots
It is the summer of 1946, at Cape Cod, Massachusetts. Billy and his annoying and overweight new bride, Valencia Merble Pilgrim, are on their honeymoon. She thinks he had girlfriends during the war, but was glad they waited to have sex and that he married her. Billy seems bored by her doting and chit-chatting .
Back to January 1945, Billy, Weary, and Lazzaro are marching with many other soldiers throughout war-torn remains of an unidentified town in Belgium, France, or Germany. Billy is flirted with by two young prostitutes while marching and bumps into Weary, stepping on his gangrene-riddled feet from wearing no combat boots. Lazzaro is furious and beats up Billy for it. Two German officers spot Billy for his clumsiness and bring him over to pose for a photo. Simultaneously, the portrait flashes forward to 1955-1958 with Billy and his family dedicating a new Ilium Optometry Center. Afterwards, an ill, senile, and shell-shocked Colonel named Wild Bob is escorting the men onto the train bound for a POW camp and fails to realize his men are not there. Billy enters the boxcar and goes to sleep. After pulling the covers on his head, it is the Spring of 1946 and he is in a veterans hospital being treated, allegedly for shell-shock or a nervous breakdown. His southern-accented and sweet-natured mother is talking to fellow patient, Elliot Rosewater of Billy's experiences. Soon afterwards, Billy is back in the boxcar with fellow soldier Weary blaming him for his death from gangrene. Paul Lazzaro cradles him in his arms and he dies. Billy finds himself back in the veterans hospital being given shock treatment.
The steam locomotive train pulls up to a POW camp somewhere in Germany. Billy is given a blue, fur-collared overcoat way too small for him by German soldiers as a joke. The men are processed by a German officer and led into a shower room to be deloused. Afterwards, Billy finds himself as a little boy of about 6 or 7 in the shower at the YMCA and his father takes him out of the shower and throws him into the pool to "sink or swim".
Billy and other soldiers are being marched to the mess hall and given a jovial welcome by English officers singing "The Yanks are Here". They are led into a dining room decorated with candles and with a potluck of potato soup, hot bread, pies, and marmalade. The English officer escorting Billy tells him the coat was a joke and to wear it with pride and how to hold his head high, despite the deplorable circumstances. Billy passes out at the suggestion.
With the tune of the Andrews Sisters singing Johnny Fedora, Billy is at his new home in Ilium in spring and summer of 1947 playing with his new puppy, Spot, with his wife calling him for dinner twice. There is a party going on at his house a later night celebrating his new baby daughter, Barbara. He's obviously feeling out of place at the party with disinterested attendees and his wife chewing him out for the dog peeing on her leg. He takes the dog outside, sits at the lake, and sees a strange occurrence in the night sky, a beam of light coming to him, then leaving.
It's back to the POW camp. Paul Lazzaro threatens Billy for Weary's death, but fellow soldier Edgar Derby intervenes. Derby is a middle-aged man of 44 years of age that gave up his job as a trade school teacher in Boston to fight in the war. He is a father figure to Billy and the two immediately form a close bond and friendship. Derby goes through Billy's coat and finds a partial denture and diamond of at least 2 carats.
It is Billy and Valencia's anniversary at their home in the summer of 1964. He gives his wife a ring made by the diamond found in his coat. Billy is bored by the crowd and retreats inside his home. He catches his son in the bathroom looking at a porn magazine and scolds him for it. But afterwards, Billy looks at the magazine himself, smiling with delighted interest at the centerfold of Montana Wildhack and goes to the bedroom with it.
Billy finds himself back at the POW camp in the briefing room with the rest of the soldiers to be told about the men's new assignment in Dresden and how lucky they are. Edgar Derby is nominated as their leader. Simultaneously, when Derby gives an acceptance speech, Billy is at a Lions Club meeting at his hometown in 1957 giving an acceptance speech.
It's about 1964 or 1965 and Billy and his family are watching a soft-core porn flick with Montana Wildhack in it. Billy's son enjoys it and his wife is outraged at the filth. Billy pays no attention to her and is engrossed in it.
Billy and fellow soldiers are in a boxcar on their way to Dresden and Derby is going over with him a letter he wrote to his wife about his service and about his pride in his son also serving in the South Pacific.
About 1965 or 1966, Billy and his wife pull up to a cemetery with a police officer that caught his now-delinquent son and others vandalizing the tombstones and offers to pay off the officers for the damages.
The soldiers pull up to the train station at Dresden, being led by an elderly German officer and several teenage proteges under his wing. They are marched to their new quarters through the beautiful city. A group of kids surround Billy while they are marching and an outraged elderly German civilian slaps him in the face, believing he is insulting his people with the coat he is wearing.
It is February of 1968. Billy and fellow optometrists, to include his father in law, are about to take a chartered flight to Montreal for a convention. Billy sees visions of skiers in the crowd when waving goodbye and tells the pilots they need to stop the plane, because it will crash. They refuse to acknowledge, but the plane does crash
Back to Dresden, the elderly German officer tells them of their quarters, Slaughterhouse Five, where they will be staying and what to shout in German in case of emergency.
Billy is buried in the snow in the Green Mountains and a group of skiers find him bloodied and buried in the rubble.
Billy's wife frantically pulls her 1967 Cadillac out of the driveway after hearing the news and comes to his rescue. She is so distressed that she misses her turn, backs into a Mercedes, drives the wrong side of the road, and causes numerous damage in vehicle accidents. She escapes the police, gets on the right side of the road, and goes forward, despite the fact the exhaust is ruined and spewing carbon monoxide. There is a brief flashback of Billy giving his wife the car for her birthday maybe a year or two earlier. Then the car pulls up to a hospital in Vermont and she crashes it into the garage, passed out from the carbon monoxide. Two nurses rescue her and bring her inside, with the gurney she's on passing the one Billy is on.
Billy is being operated on and simultaneously, he and the fellow soldiers are in their slaughterhouse quarters being briefed about their working assignments by the German officer and daily routine of work. After the operation is over, the doctor that operated on Billy greets his daughter Barbara that everything will be okay. Barbara's husband Stanley comes over to her to give her the news that her mother died from carbon monoxide poisoning earlier.
Billy is in his room recovering with an arrogant professor and historian for a roommate named B.C. Rumfoord telling his much-younger wife about being stuck in a room with such a weak and worthless man. He's writing a story on the bombing of Dresden and Billy says in a daze he was there, but Rumfoord couldn't care less. Simultaneously, Billy is blathering in German that he's an American Prisoner of War and Slaughterhouse Five. Rumfoord loses his temper and tells Billy the bombing was justified, while simultaneously, Billy as a young soldier is walking amidst a crowd of cheerful kids just hours before the bombing.
The night of the bombing at dinner, an American dressed up in a Nazi uniform with American flag decor named Howard Campbell, is summoned to recruit the men for the Free American Corps, which is an allied unit with the Germans and that the Communists and Jews are their enemy. Derby calls him out on it for what a filthy traitor he really is, but before he can say anything more, an alarm goes off for the city and the men are ordered to evacuate to an underground cellar for shelter. Dresden gets bombed.
In March 1968, Billy is taken home by his daughter Barbara and she pleads with him to stay with she and her husband, but he refuses. He is senile, listless, and apathetic at this point. He takes his elderly dog Spot and shuts the door in her face.
The bombing is over and the soldiers go up the stairs to inspect the damage. Simultaneously, Billy is walking upstairs in his posh estate to his bedroom with his dog in his arms. The men walk outside. A teenage German soldier guarding their group denounces the bombers as filthy pigs in German and runs to rescue his family, who were already killed and he burns to death searching for them.
Billy is laying in bed at his home with Spot and his son Robert has come to visit him. The former delinquent is now a sharp Green Beret in the Army fighting in Vietnam home on emergency leave. Robert is caring of him and trying to have a conversation, but Billy is preoccupied with himself, looking out the window at the night sky, and uninterested at his visiting, but assures him he's proud of him. Right after Robert leaves, the beam of light he saw in the sky while at the lake at his house in 1947 reappears and takes him away. He and his dog Spot are whisked away to a geodesic dome on the planet Tralfamadore. He's confounded as to his appearance there. The Tralfamadorian elder tells him he can't see them because they live in the Fourth Dimension and that he can't leave the dome. No reason why he is there, he just is.
Billy and the American soldiers are ordered by the elderly German officer to process the corpses from the rubble of the bombed Dresden city and to collect their personal remains. They are given a direct order that any looting or stealing will result in firing squad. While Billy and the soldiers are collecting the bodies, he's on Tralfamadore telling the elder about the bombing and how it affected him, but he's comforted and assured that everything that happens always has and always will happen and that the past, present, and future are always happening at the same time in their world, which also gets destroyed and destroys the entire universe because of a mishap with one of their test pilots.
Porn actress Montana Wildhack has now been added to the exhibit with Billy in the dome and she's scared to death at first not knowing what's happening. The Tralfamadorian elder insists that they mate, but Billy insists on being a Gentleman with her and does not follow the order. But she lets him go to bed with her and they make love.
Some days later after the bombing, Derby finds an undamaged figurine in the rubble that is an exact replica of one his son broke before. He's caught by German officers and shot to death by firing squad. Billy tries to stop it to no avail.
Billy is back on Tralfamadore with Montana in her new wardrobe. He tells her of his wife, that the thing he liked best about her was her pancakes. They want to have a baby together.
It is back to March 1968 when Billy's daughter was frantically searching for him in his house. He, his daughter, and son in law are at the dining room table and she really thinks he's lost his mind about Tralfamadore and his son in law suggests seeing a psychiatrist. He assures them that the Tralfamadorians do not see past, present, and future the way Earthlings do. And also reveals to them the disappeared porn star Montana Wildhack is the love interest there and that he's seen his death.
It is an unspecified time, perhaps the early 2000's. An elderly Billy Pilgrim in his 80's addresses a crowd at a high rise in Philadelphia about Tralfamadore and their lack of concept about time. And that a fellow soldier from World War 2 is about to kill him. Paul Lazzaro is now also a very elderly man that lives in the area shooting him sniper-style and instantly killing him.
Billy wakes up to find himself amongst the remains to Dresden in April 1945 with Lazzaro and fellow soldiers attempting to steal a grandfather clock. He's assured all the Germans have left, but when in the process of stealing, Lazzaro and the others leave, with the clock toppling on Billy. It turns out the German side of the war is over and Russian soldiers give Billy a drink to celebrate, which he gags
Billy and Montana have a baby on Tralfamadore, with the entire planet celebrating with an array of fireworks