A group of heavily armed mercenaries, led by Hanover, hires boat captain John Finnegan and his crew to take them to an undisclosed location in the South China Sea. Finnegan, unaware of the group's true intentions, soon realizes that they are planning to hijack and rob a luxury cruise liner, the Argonautica, which has mysteriously lost contact with the outside world. As they board the seemingly deserted ship, they discover signs of a desperate struggle and encounter Trillian, a captured thief who had been imprisoned by the ship's crew. The team is quickly attacked by grotesque, tentacled sea creatures that have infested and decimated the liner's passengers and crew.

Finnegan, Trillian, and the mercenaries are forced to work together to fend off the relentless creatures while seeking a way to escape the doomed vessel. Tensions rise as their numbers dwindle and secrets about their employers’ motives come to light. Amidst the chaos, they navigate through darkened corridors and flooded compartments, racing against time and the growing threat of the creatures devouring them all. Their survival instincts are pushed to the limit as they try to find a way off the ship before it succumbs entirely to the deadly marine predators.