It's New Year's Eve and festivities have begun aboard the luxury cruise ship Poseidon, at sea in the North Atlantic. One of the finest vessels of its kind, Poseidon stands more than 20 stories tall, boasts 800 staterooms and 13 passenger decks.

Tonight, many of the ship's guests have gathered to greet the New Year in style in the magnificent main ballroom. However a Rogue Wave, a monstrous wall of water over one hundred feet high, is bearing down on them with tremendous speed. The wave strikes with colossal force, pitching the ship heavily to port before rolling it completely upside down; supports collapse, broken gas lines ignite flash fires and lights fail, leaving vast sections of the ship in darkness and chaos.

In its aftermath a few hundred survivors are left to huddle in the still-intact main ballroom, now resting below the waterline. One man, professional gambler Dylan Johns (Josh Lucas), prefers to test the odds alone. Ignoring orders, he prepares to exit the Ballroom and find his own way to safety, but is collared by nine-year-old Conor (Jimmy Bennett), who asks that Dylan take him and his mother Maggie (Jacinda Barrett) along.

Fast behind them is Robert Ramsey (Kurt Russell), anxious to search for his daughter Jennifer (Emmy Rossum) and her fiance Christian (Mike Vogel).