The stories of several people unfold on a magnificent ship, Poseidon. Heroine Jennifer Ramsey, the 19-year-old daughter of a patronizing former New York mayor, and her fiancé Christian are finding it difficult to tell her father that they're engaged. A single mother and her son Conor run in (literally) to Dylan Johns, a professional gambler and hit it off right away. Elena has agreed to be a steward's entertainment for the cruise if he takes her to New York to see her injured brother. Architect Richard Nelson is drinking himself into a stupor after his boyfriend ditched him. When a rogue wave hits and the ship overturns, the captain tells the surviving passengers that the ballroom is an air bubble and that they will be safe until help arrives. Dylan isn't so sure and sets off to look for an avenue of escape. Conor asks Dylan to take he and his mother. Richard knows that the boat cannot stay afloat upside down. Ramsey insists on going with to find his daughter in the nightclub. The five people take the steward Marco to help them find their way to the bottom/top. In the nightclub, most are dead after being electrocuted by the numerous lights. Survivors are Jennifer, Elena, Lucky Larry and Christian, who is caught under a light. The two groups of adventurers converge and have to fight fire, electricity, tight spaces, elevator shafts and most of all, water.