Plot
While aboard a houseboat on Crystal Lake, teenager Jim tells his girlfriend Suzi the legend of Jason Voorhees, before playing a prank on her with a hockey mask, similar to Jason's old mask, and a prop knife. The boat's anchor damages some underwater cables that shock and revive Jason, who was dragged down there by the spirit of Tina Shepard's father. He sneaks on board, takes the mask, and kills Jim with a speargun before impaling Suzi.
The next morning, the SS Lazarus is ready to set sail for New York City with a graduating senior class from Lakeview High School, chaperoned by biology teacher Dr. Charles McCulloch and English teacher Colleen Van Deusen. Colleen brings Charles's niece Rennie Wickham along for the trip despite her aquaphobia, much to his chagrin. Jason sneaks on board and kills rock star-wannabe J.J. with her guitar. That night, a young boxer who lost his match to champion Julius is killed by Jason in the ship's sauna. Rennie, searching for her pet Border Collie Toby, discovers prom queen Tamara Mason and her friend Eva doing drugs. Charles nearly catches them moments later, and Tamara pushes Rennie overboard, believing she told on them. She then uses video student Wayne Webber to record Charles in a compromising situation with her but rejects Wayne's advances afterward. Jason kills Tamara with a shard of a broken mirror after she showers.
Rennie sees visions of a young Jason in different forms throughout the ship. Jason kills Admiral Robertson and his first mate Jim. Rennie's boyfriend and Captain Robertson's son, Sean, discover them and tell the others before calling for an emergency. Eva finds Tamara's body and flees. Jason chases Eva into the disco room, where he strangles her to death on the dance floor. The students agree to search for Jason while Charles decides that the deckhand is responsible. However, the deckhand is found with a fire axe in his back. Jason tosses student Miles Wolfe into the radio transmitter tower to his death, and Julius is knocked overboard. In the hold of the ship, Wayne comes upon J.J.'s body and is thrown into an electrical box by Jason. Wayne's corpse catches fire and causes the ship to take on water. With the other students that were left in the disco room seemingly dead, Charles, Colleen, Rennie, and Sean escape aboard a life raft and discover that Toby and Julius are still alive. The five then row away as the Lazarus sinks.
They row to New York City, where Jason stalks them through the streets. Rennie is kidnapped by Homes and Jojo, a pair of drug addicts, and the group splits up to find help. Julius fights Jason on a rooftop but becomes exhausted after Jason does not go down after a series of punches, and then gets decapitated by a single punch from Jason. Rennie escapes from Jason when he kills the punks that kidnapped her. She runs into Sean, and they reunite with the teachers and the NYPD before Jason kills the officer who is helping them. Rennie crashes a police car after a vision of Jason distracts her. Colleen is incinerated in the car when it explodes, and it is revealed that Charles is responsible for Rennie's fear of water, having pushed her into the lake as a child. They leave him behind, and Jason drowns him in a barrel of toxic waste.
Jason chases Rennie and Sean into the subway, where Sean incapacitates Jason by pushing him onto the third rail. When Jason revives, he chases them through Times Square to a diner and then into the sewers, where they encounter a worker. He warns them that the sewers will be flooded with toxic waste at midnight. Jason appears and kills the worker before knocking Sean unconscious. Rennie throws a vat of toxic waste into Jason's face, causing his skin to melt away. She and Sean climb a ladder as Jason staggers after them. The sewers flood, and Jason is reminded of his childhood drowning and vomits water. The wastewater overcomes Jason, washing his body away. When the water recedes, Rennie once again sees her vision of Jason as an unconscious child for the final time, finally conquering her longtime fear. Sean and Rennie return to the street, reuniting with Rennie's dog Toby in Times Square.
