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...

A volcanic eruption in Iceland sends a glacier towards North America, causing everything in it's path to freeze. A family man struggles to escape the onslaught of the coming ice age.