Alex Shaw, portrayed by Jason Patric, finds himself embroiled in an exhilarating motorcycle chase after a vehicle loaded with stolen goods. After successfully apprehending the driver, his plans take an unexpected turn when his girlfriend, Annie, accidentally collides with him during her driving test. To make amends for his earlier deception—where he claimed to be a beach cop instead of revealing his reality as a member of the SWAT team—Alex surprises Annie with a romantic getaway to the Caribbean aboard the luxurious cruise ship, Seabourn Legend.
However, their idyllic vacation quickly spirals into chaos when the sinister passenger, John Geiger (played by Willem Dafoe), orchestrates a series of explosions designed to cripple the ship's communication systems. The next evening, Geiger commits an even more heinous act by throwing the captain overboard. He seizes control of the ship's computer systems and issues a chilling ultimatum to the first officer, Juliano, compelling him to evacuate while simultaneously plundering the ship's vault for valuables.
As panic unfolds, a young deaf girl named Drew becomes trapped in an elevator, while a group of terrified guests becomes ensnared behind locked fire doors as smoke engulfs the corridor. In a desperate attempt to evade the chaos, Alex and Annie rush to board the last lifeboat, only to have the winch malfunction as the ship begins to move. Acting quickly, Alex leaps onto the lifeboat to save passengers on the brink of falling, while Annie teams up with Juliano to assist others returning to safety on deck.
Realizing the true extent of Geiger's malevolence, Alex and Juliano arm themselves with skeet guns and make their way to Geiger's cabin, only to find their efforts thwarted as Geiger triggers more explosives remotely. Meanwhile, Annie discovers the group trapped behind the fire doors with the ship's photographer, Dante, and bravely uses a chainsaw to free them. Alex, taking charge, orders navigator Merced to flood the ship and enact emergency measures.
As the ship fills with water, resolved to rescue Drew, Alex spots her on a monitor and rushes to her aid. He confronts Geiger as he attempts to escape the vault, but the villain cunningly shuts a fire door in Alex's face. Geiger's menacing voice echoes through the intercom as he reveals his scheme to use the ship's autopilot for revenge, after being dismissed due to a debilitating copper poisoning sickness.
With the ship on a catastrophic collision course with an oil tanker near Saint Martin, Alex resolves to halt the impending disaster by diving beneath the vessel and jamming the propeller with a steel cable. However, Geiger retaliates by sabotaging the cable winch, complicating Alex's mission. In a desperate move, Geiger captures Annie and escapes on a boat.
To avert the catastrophe, Alex and Dante rush to the bilge pump room, employing the bow thrusters to maneuver the ship away from its dangerous trajectory. They manage to avoid a catastrophic collision, but the ship subsequently crashes onto an island, bringing to a halt the wild ride. In a spectacular rescue attempt, Alex jumps off the ship to save Annie and commandeers a speedboat from Maurice (Glenn Plummer), forcing him to aid in the chase.
The tension escalates when Geiger takes Annie onto a seaplane, prompting Alex to take swift action. He heroicically shoots the plane with a spear-gun, reeling himself in through the water. His daring effort culminates in an intense confrontation where he manages to rescue Annie just as the plane spirals out of control, ultimately crashing into the oil tanker, resulting in a massive explosion.
With the peril behind them, Alex and Annie return to shore aboard Maurice's boat, where Alex sweetly presents her with a wedding ring, asking if she would consider "wearing it for a while." Overwhelmed by love and adventure, Annie gladly accepts, sealing their bond amid the remnants of their chaotic escape.
