Late one night, on one of the many beaches of Amity Island off the coast of New England, local teenagers throw a bonfire party, tossing back the booze and playing music. Chrissie Watkins (Susan Backlinie
), a beautiful blonde, catches the eye of Tom Cassidy (Jonathan Filley
) and leads him away from the frivolities towards the water where she begins to strip down. She invites him for some moonlit skinny dipping and dives into the water as Tom struggles to undress on the shore. Inebriated, Tom collapses and passes out on the sand. Chrissie continues to swim out to deeper waters when she feels a sharp tug on her leg. Confused, she gasps in panic as she is tugged again before being pulled under water. She breaks the surface, screaming as something thrashes her around violently. She screams for help again before submerging one last time and then the water is still.
Amity Island is a small, beachside community that prides itself in its humble traditions and popular oceanfront. Despite the population of locals on the island, the community depends on tourism as a major source of economic support and waits eagerly for each summer to arrive when herds of mainlanders come to savor Amity's shores.
Martin Brody (Roy Scheider
), the new Chief of Police, receives a call at home regarding Watkins' disappearance. Following the report made by Tom Cassidy that she was last seen off the coast, Brody goes to the beach with his deputy Jeff Hendricks (Jeffrey Kramer
) to search for clues. They don't need to look very long; within a few moments Hendricks stumbles upon Chrissie's mangled corpse.
At the police station, Brody waits for the coroner's (Robert Nevin
) report at his desk while the secretary relays the crime reports of the day; nothing more serious than a few kids 'karate-chopping' picket fences. The coroner then calls with his report. Brody hangs up and contemplates for a moment before typing the cause of death on Chrissie's report: 'Shark attack'. Unwilling to waste any time, he goes to the local hardware store and gathers supplies for making signs to close the beaches. His intentions are quickly noticed by Mayor Vaughn (Murray Hamilton
) who attempts to sway Brody's notion that a shark was directly involved in Chrissie's death. He explains that she could very well have swam out too far and gotten tired before being hit by a boat's propellers. During a town meeting, Brody tries to reassert his belief that Chrissie's death was caused by a shark and that he wants to close the beaches for the safety of the public, much to the dismay of the island's business owners. Vaughn, however, garners the coroner's support who admits that Chrissie could have been killed by a boat propeller. Vaughn reiterates to Brody that he doesn't want to act too hastily. Closing the beaches would sentence Amity Island to a dreary summer without tourists and they cannot afford to lose that source of income, especially with the Fourth of July approaching.
Over the course of the next couple of days, tourists flock to the island, brought over from the mainland by ferry. One particular day, Brody sits on the beach, scanning the water nervously as people frolic in the surf, splashing and calling to each other. A young man ( nm5026721
) plays fetch with his labrador retriever in the surf. An elderly man wearing a swim cap, Henry Wiseman (Alfred Wilde
), approaches Brody and chides him about his apparent fear of water. "Thats some bad hat, Harry," Brody replies, annoyed. Young Alex Kintner (Jeffrey Voorhees
) takes his inflatable, yellow raft and asks his mother (Lee Fierro
) if he can take it out in the water. With her consent, he rushes into the surf. While Brody continues to keep watch, the beachgoers continue their fun, splashing loudly. The young man who had been playing with his dog calls to the unresponsive pooch, the fetching stick floating in the water. All at once Brody notices a large, grey object emerge out of the water and overturn the young boy on his yellow raft. Alex is tossed into the water and pulled under as his blood turns the sea red. The other swimmers begin screaming and leave the water as Brody ushers them back to shore. Mrs. Kintner approaches the water's edge, calling for her son. The only response is the lap of waves on the shore, pushing Alex's torn and bloody raft onto the beach.
Shortly after, Mrs. Kintner issues a $3000 reward for the capture of the shark and a meeting is held between the town's business owners, attended by Mayor Vaughn and Brody. Brody assures the townspeople that they are assigning extra deputies and bringing in an expert from the Oceanographic Institute for advice on the matter but the main concern in town is if the beaches will be closed. Brody's 'yes' is responded with a string of criticism but Mayor Vaughn quickly interjects that the beaches will be closed for only 24 hours. The uproar of the townsfolk is suddenly cut short by the screeching sound of nails on a chalkboard behind them. Fisherman Quint (Robert Shaw
) remains seated as he calmly explains that a shark like this is not one to be trifled with and he has no interest in such meager compensation. He offers to capture and kill the shark himself for $10,000 which no one stands to offer. Quint quietly leaves, a wry smile on his face.
Brody returns home and, the following day, tells his eldest son Michael (Chris Rebello
) that he's not to go anywhere near the water. Ellen thinks him to be acting a bit too harshly, even when Michael tests his new sailboat in the shallow water in front of their home. When she sees a picture in a book that Brody's holding of a shark attacking a small boat and puncturing the hull, however, she shouts for Michael to listen to his father and get out of the water.
That very evening, two men decide to take matters into their own hands and fashion a large hook baited with a pork roast. They toss it out from a dock and it attracts the attention of the shark. However, their attempt to be heroes nearly turns fatal when the dock they've secured the line to is detached and pulled out into the water by the beast, taking one man with it. He fortunately manages to swim back to his friend as the dock eerily turns and follows him back to shore, eventually drifting back on its own, harmless.
Amateur shark hunters and fisherman from all over descend on Amity Island hoping to get a claim to the $3000 reward that has apparently been advertised expansively by Mrs. Kintner. They crowd the waters surrounding the island, creating some tension to local swimmers. Among the horde of newcomers is Matt Hooper (Richard Dreyfuss
), who has arrived from the Oceanographic Institute. He is escorted by Brody to examine and give his professional opinion on the remains of Chrissie Watkins. After viewing the body and recording his observations, a visibly shaken Hooper angrily informs Brody and the coroner that no boating accident killed Watkins. "It was a shark," he states defiantly.
Meanwhile, some of the local fisherman have successfully caught a large shark and haul it back to town where the body is strung up for all to see. The townsfolk are ecstatic to see such a large find and are overjoyed and convinced that the killer has been caught. However, most are ignorant to the species until Hooper and Brody arrive. Hooper takes a look at the shark and informs everyone that it's a tiger shark and that the bite radius does not match up with the marks he found on Chrissie's corpse. Mayor Vaughn objects and claims that the beaches should be reopened but Hooper maintains that he won't be completely satisfied until he can cut open the shark for more conclusive evidence. Vaughn, however, is not eager to do so in public at the risk of seeing the 'little Kintner boy spill out over the dock'. At that moment, Mrs. Kintner arrives on the scene, clad in a black, mourning dress. She addresses Chief Brody and slaps him across the face, informing him that she found out about Chrissie's death and accuses him of keeping the beaches open and letting people swim when he knew there was a shark out there. When she leaves, Vaughn consoles Brody and tells him that Mrs. Kintner is wrong. "No she's not," replies Brody.
Unsatisfied with how his findings took to the water, Hooper visits Brody for dinner that night, sharing his theories with Ellen Brody (Lorraine Gary
) who is none too pleased about the presence of a large shark in the area but stands by her husband's intuition. Hooper discusses the possibility of a rogue shark in the area while Brody chugs his wine. Hooper explains that a rogue shark will often claim territory to an area where the feeding is good and will remain there until the food source is gone. Brody agrees to take Hooper down to the docks to cut open the tiger shark and find out, once and for all, if this is indeed the shark that's been terrorizing the island. Hooper cuts out the stomach and, in a mess of bile and seawater, recovers a few fish, a tin can, and a license plate from Louisiana that confirms his suspicions that the shark swam up to Amity from warmer waters. There is, however, no sign of any human remains and Hooper tells Brody that he's 'still got one hell of a fish out there' and measures out a space with his hands to show how big it's mouth might be.
That night, Brody and Hooper continue their investigation and Hooper decides that some reconnaissance out on the water is needed, much to Brody's dismay. With sonar equipment installed on his boat, Hooper drives the boat out to deeper waters until the sonar detects a large object just ahead of them. Aiming their lights out, they find a half submerged fishing boat that Brody recognizes as Ben Gardner's (Craig Kingsbury
), a local fisherman. Hooper bravely opts to take a closer look underwater and dons scuba gear despite Brody's protests. Hooper dives under and examines the hull of the ship, soon discovering a gaping hole in the side where a rather large tooth is embedded. As he peers closer into the hole, the ghostly torso of Ben Gardner appears, his one remaining eye gazing out in horror. Terrified, Hooper panics and drops the tooth as he scrambles back onto his own boat.
The next morning, he and Brody attempt to reason with Mayor Vaughn, who seems more concerned with an act of vandalism on one of Amity's billboards. The graffiti sprayed on the image of a woman swimming altered her face to one of horror and included a large, black fin following her in the water. Hooper tries to convince Vaughn that, based on his findings, the proportions on the drawing are actually correct and that, with the evidence of Gardner's boat and his remains towed back to the island and the tooth he found, the existence of a large, killer shark cannot be ignored any longer. Vaughn is adamant, however, that the beaches will remain open for the Fourth of July and tells Hooper that losing the tooth is very convenient for him and he most likely wants nothing but the publicity to get him in the National Geographic. Hooper can only laugh at the insult as Vaughn walks away.
On July 4th, the beaches are flooded with mainlanders and tourists. Brody and Hooper have their hands full keeping order and making sure that enough security is patrolling the beaches, including boats full of patrolmen with rifles and shark spotters. However, the increased precautionary measures create tension among the beachgoers, making them hesitant to enter the water. Vaughn notices this and convinces one of his local friends to take his wife and grandchildren out. They do so nervously but this encourages more people to enter the water and releases the tension. Brody patrols the beach while Ellen takes care of their youngest son, Sean (Jay Mello
). Michael and a friend begin to take his new sailboat out but Brody tells them to take it to the estuary where it's safer. Suddenly, a shark fin appears in the water and everyone begins to scream in panic, stampeding back to the shore and knocking a few hapless swimmers over. Vaughn watches in disbelief as Brody oversees the situation. The patrol boats quickly scramble towards the fin but discover that it is false; a prank pulled by a couple of boys in snorkel gear.
As the chaos winds down, a girl painting on the edge of the estuary sees a dark fin with the shadow of its body beneath it. She cries out 'shark' but the general reaction is desensitized by the fin hoax. Brody responds to the call and quickens his pace when Ellen reminds him that Michael is in the estuary. Michael and his friend sit in their sailboat and are approached by a friendly man (Ted Grossman
) in a rowboat before both crafts are suddenly capsized. Michael surfaces and watches in horror as the man attempts to return to his rowboat, only to be eaten alive by the massive shark. His severed leg sinks to the bottom of the estuary and the shark swims back into open water. Michael and his friend are brought safely ashore, though Michael is unconscious from shock. He is later brought to the hospital and Brody confronts Vaughn in the lobby and demands that immediate action be taken now that there's no doubt in anyone's mind that they have a killer shark around the island. Vaughn, shaken and distressed, realizes his mistakes and tells Brody that his family was on the beach too. He allows Brody to do what's necessary.
With Vaughn's signature approval, Brody hires Quint to hunt the shark, promising the fee he'd demanded earlier. At Quint's boathouse, Brody and Hooper discuss with him the terms of the voyage. From the start, Quint looks down upon Hooper for his academic prowess and believes that it will not serve him any good out on the raw sea. However, Brody insists that both he and Hooper will accompany Quint despite his belief that they have no nautical experience -- Hooper mentions that he's crewed three TransPac sailboats, justifying his experience at sea. When Hooper ties a 'sheep shank' knot with ease, Quint relents. Come morning, they meet at the docks and prepare Quint's ship, Orca, for the voyage. Hooper brings his own hi-tech equipment including harpoons, tracking devices, scuba gear and tanks, and a shark-proof steel cage, though Quint is less than impressed with the safety guarantee on the cage.
Once at sea, they attempt to attract the shark by chumming the water with fish guts and blood. Hours pass and Quint sets up a baited line with piano wire and fashions it to a rod secured against a fishing chair. He waits as Brody practices his knot work and Hooper plays cards. Quint's line begins to pull and he eases into his chair, quietly fastening straps to his shoulders and adjusting the rod. Just when Brody successfully knots his rope, the line jerks forward, taken by something far under. Hooper projects that the taker might be a sports fish, like a marlin, but Quint assures them that it's 'their' fish. The line is pulled under the boat and Quint marvels at the fish's clever move until the line completely snaps. Quint and Hooper argue over what might have taken the line and Quint suggests that Hooper doesn't have the education to admit his error; that no regular fish could have severed piano wire. Hooper makes a series of dirty faces and climbs up to the bridge.
Later on, and still with no sign of the shark, Brody is assigned to chum duty, a job that he has come to detest. As he smokes a cigarette, he scoops out the chum and blindly throws it into the water while casting Quint a contemptuous look. Suddenly, the massive shark surfaces, its mouth agape, but only for an instant. Brody quickens to a stand, having seen enough of the shark to be fearful. He backs slowly into the cabin and tells Quint that he's 'going to need a bigger boat'. At that moment, Hooper sees the shark begin to circle the boat and Quint rushes out to see it. He wages a 25 footer, three tons and orders Hooper and Brody to action. Quint grabs his harpoon gun and instructs Hooper to tie the other end of the rope attached to it to one of the large, yellow bins on the boat. Quint shoots a total of three harpoons, each trailing a yellow bin, into the shark but it doesn't show the slightest bit of fatigue and easily disappears below the surface as Hooper manages to attach a tracking device to it.
Quint is at first disdainful towards Hooper after the shark escapes but, that night, the men bond after sharing drinks and comparing scars they've received by some of the deep's more dangerous creatures. Hooper and Quint realize they have more in common than they thought and begin to bond. Brody points to one scar on Quint and he reveals that he'd had a tattoo removed, a tattoo that represented the US Navy cruiser
'Indianapolis'. He tells the story of how he was on the ship the day two Japanese torpedoes blasted a hole in the side large enough to sink the ship in minutes. Quint and some 1,100 men went in the water but, by the time rescue arrived, only 300 survived, some dying of thirst or exposure but most getting attacked and eaten by sharks. Quint's hatred for sharks is evident, describing them as lifeless with doll's eyes and how terrible it was to see and hear the men around him picked off. Worse yet for him is the survivor's guilt he feels. When help finally did arrive, Quint vowed never to wear a life jacket again. As Quint finishes his story, the men sing a sea shanty as the three yellow barrels break the surface of the water outside. As they finish their song, the boat is bumped repeatedly and violently by the shark causing minor leaks. Quint runs onto deck and fires shots at the fleeing shark, evident only by the barrels trailed in its wake and they quickly disappear beneath the waves.
The next day the hunt for the shark continues. When they spot the three barrels floating in the water, Quint instructs Hooper to collect them with a hook and secure the rope to cleats at the stern of the boat. The shark begins to swim off again and Hooper's legs are nearly crushed when the rope is pulled taught. Quint drives the boat forward at full throttle but, despite the power, the shark manages to drag the boat backwards, threatening to capsize it, until the cleats rip out of the stern. Out of options, and with the barrels no longer attached to the shark, Quint allows Hooper to try a new method. Hooper opts to submerge himself in the shark cage, hoping that the shark will swim close enough that he can inject it with a harpoon filled with strychnine nitrate. Brody protests but Hooper angrily retorts, "You got any better suggestions?" as he puts on his scuba gear.
In the cage, Hooper is ambushed by the shark which begins to rip the cage apart, making short work of the metal. Hooper loses his harpoon but is able to escape and swim down to the reef while the shark destroys the cage. Brody and Quint bring up the remains but, before they can do anything, the shark leaps out of the water, landing on the stern, crushing the transom. The boat upends and Brody and Quint hang on for dear life as the shark's jaws gnash and water fills the cabin. Quint loses his grip and slides right into the shark's mouth. The jaws come down on Quint's midsection several times and drags his lifeless body into the sea. As the Orca begins to sink, Brody retreats into the cabin and finds one of Hooper's spare scuba tanks just as the shark barrows through the side, breaking the window. Brody beats it on the nose with the tank before throwing the whole thing into its mouth. The shark backs away as Brody climbs out of the cabin and climbs onto the boat's mast with a rifle in his hand. As the shark circles again and charges Brody, now lying angled on the mast, he aims the rifle at the shark and fires off a few shots, missing. Finally, he takes close aim. "Smile, you son of a bitch," he says, and fires, hitting the tank and detonating it in a violent explosion. The force rips the shark apart and its body sinks to the sea floor as Brody laughs happily.
Brody grabs hold of a piece of flotsam as Hooper surfaces, unharmed. Together they create a makeshift raft and begin paddling back to shore as seagulls descend on the remains of the shark.
"I used to be afraid of the water," Brody admits.
"I can't imagine why," Hooper replies.