While preparing to take her autistic son Tommy on a boat trip with her friend Greg, Jess hears the doorbell ring, but no one is there. She later arrives at a harbor in Florida without Tommy, explaining he’s at school, and boards Greg’s boat. She meets Greg’s married friends Sally and Downey, Sally’s friend Heather, and Victor, a runaway teen living with Greg. While out at sea, the wind dies and a storm approaches, and they pick up a distress signal while radioing the coast guard. The storm capsizes the boat, during which Heather is swept out into the water, and the others climb onto the overturned boat when the storm clears.
They board an ocean liner as it passes; it appears to be deserted, yet there is fresh food in a dining room. Jess experiences a growing sense of déjà vu as they explore. They find Jess’s keys in a corridor near a display case for Aeolus, the ship’s namesake, leading Sally to believe Heather has also boarded. Jess soon spots someone watching them and Victor gives chase. She and Greg continue on and find “Go To Theater” written in blood on a mirror. After they part, she returns to the dining room, where the food is now rotting. Victor enters, covered in blood, and tries to kill Jess; she fights him off by aggravating a wound at the back of his head. She hears gunfire and follows it to a theater, where Greg lies dead of a gunshot. Sally and Downey tell Jess that Greg told them she shot him. They accuse her of the sending them to the theater. A burlap-masked shooter kills them from a balcony and chases Jess to an outside deck; she fights back and disarms the shooter, who tells her “You have to kill them; it’s the only way to get home” before falling overboard.
She soon hears yelling, and sees herself and the others alive on Greg’s upturned boat. After they board, Jess becomes the earlier unseen figure: she drops her keys near the display case and is spotted shortly after. She attempts to warn Victor when he catches up to her, only to accidentally impale his head on a wall hook. She flees deeper into the ship and finds dozens of duplicates of the shooter’s outfit, shotgun, her own locket, and a note saying to kill them all when they board. She takes a shotgun, intending to “change the pattern,” but the shooter, another Jess, kills the men and mortally wounds Sally with a knife.