Ellen Brody still lives in the island resort town of Amity, and her sons Sean and Michael don't work at Sea World anymore, and some time ago, Ellen's husband Martin Brody died of a heart attack that happened because he was afraid of sharks. Sean is now a deputy in Amity. One night, during the Christmas season, Sean is called to untangle a log from a buoy, and when Sean goes to the buoy, he's killed by a great white shark. After hearing about this, Michael, who is studying to be a marine biologist, visits Amity with his wife Carla and his 5-year-old daughter Thea. Wanting to get away from Amity and spend Christmas with Michael, Carla, and Thea, Ellen goes with them to their house in the Bahamas on an airplane whose pilot is Hoagie Newcombe, and Hoagie starts falling for Ellen. Michael's friend Jake, who is also studying to be a marine biologist, lives next door to Michael...

The small island resort town of Amity is trying to bounce back from the financial problems it had after becoming known as the site of shark attacks four years ago. Mayor Larry Vaughn is welcoming developer Len Peterson and his new resort to Amity. Two scuba divers are exploring the area where the Orca sank after police chief Martin Brody killed a huge shark four years ago. A shark shows up and kills the two divers, but not before one of the divers takes a close-up picture of the shark's eye, and sometime later, while a mother is driving a boat that's pulling her water-skiing teenage daughter, the shark kills the daughter and causes the mother to accidentally blow up the boat, then a killer whale is found on the shore with a huge bite on it. After Brody sees this, he knows there's another huge great white shark in Amity's waters, but Vaughn and Peterson explain these attacks away as non-shark accidents...