On Amity Island, Chief Martin Brody has died from a heart attack, although his wife, Ellen, says it was from fear of the shark. Brody’s younger son, Sean, is now a sheriff’s deputy and engaged to marry a woman named Tiffany. Sean Brody is sent into the harbor to clear a log from a buoy a few days before Christmas. As Sean leans over the boat to move the log, a massive great white shark attacks, biting off his arm. The shark attacks the boat repeatedly, pulling Sean into the water. Sean holds onto the log, but the shark pulls him underwater, killing him. Ellen Brody’s older son, Michael, flies in for the funeral with his wife, Carla, and their five-year-old daughter, Thea. They invite Ellen to return with them to the Bahamas. Ellen agrees, but tells Michael to give up his job as a marine biologist. She does not want her family anywhere near the water. Ellen has nightmares about the shark attacking her in the water and grows agitated when she sees her granddaughter, Thea, playing on the dock, telling her to avoid the water. Michael and his colleague, Jake, are working on a research assignment funded by the Bahamian Fishery Department. They have three more months of studying sea snails known as conches, but have run out of money. Jake proposes they apply for a grant from the Office of Naval Research, but Michael vetoes the idea, suggesting that the ONR puts bombs on dolphins. Ellen Brody spends time with a local pilot named “Hoagie.” She tells him the shark is coming after her, following her family, and wants revenge. Hoagie tries to distract her by taking her for a ride in his small four-seat plane and teaching her how to fly. As they spend time together, Ellen begins to fall in love with Hoagie. Michael Brody is glad his mother’s life in brightening, but concerned that Hoagie is not the right man for her. One day, as Michael examines the conches on the ocean floor in a small, one-person submarine, a giant great white shark swims by. The shark attacks their research boat, Neptune’s Folly, then swims away. Michael and Jake are stunned by the attack, noting that great white sharks do not like warm water. Michael asks Jake not to say anything about the attack to his mother, however Ellen senses the shark is nearby. Jake wants to study the shark, suggesting they place a tracker on it. The boat’s crew drops bloody chicken meat in the water to lure the shark. When the shark comes for the bait, Jake shoots it with a spear, attaching the electronic tracker. After the shark swims out of tracking range, Michael gets back in the small submarine to explore the ocean floor. The shark returns and attacks Michael in the sub. Although the shark bites Michael’s arm, he gets out of the sub safely and swims along the bottom of the sea with an oxygen tank. The shark chases him. Michael swims into an old wrecked ship on the sea bottom to get away, but the shark follows him inside. Michael escapes by quickly swimming to the surface. As this happens, Ellen again senses the shark is nearby. Michael’s wife, Carla, a sculptor, creates a sculpture for the beach. At the dedication ceremony, the shark attacks a rubber raft Thea Brody and some other children are riding in the harbor. The shark bites and kills the adult riding on the raft, but the children make it to safety. Ellen gets in Neptune’s Folly and goes after the shark, intending to kill it. Hoagie takes Michael and Jake in his plane to search for her. Hoagie tells the men that Ellen is convinced the shark is following the Brody family. Ellen spots the shark and intends to ram the boat into it. Hoagie lands the plane on the water near the boat. Michael and Jake swim to the boat, but the shark attacks the plane. The plane sinks with Hoagie in it, but he escapes and swims to the boat. The tracking monitor indicates the shark is still nearby. Jake puts together a bomb and shoots it into the shark’s mouth. However, the shark grabs Jake in its mouth, taking him underwater. They assume that Jake is dead. Michael sets off an electronic impulse to the bomb. The impulse agitates the shark, causing it to flail about in the water, and attack the boat. The shark hits the bowsprit and explodes, causing the boat to rip apart. Ellen, Michael and Hoagie fall into the water, but a moment later, a badly injured Jake surfaces. Michael rescues Jake, while Ellen hugs Hoagie. A few days later, Hoagie flies Ellen back home. She is content, knowing she and her family are safe from the vengeful shark.