The S.S. Poseidon, a luxury ocean liner, is on its final voyage, this sailing from New York to Athens, before it heads to the scrap yard. Against his protestations about the dangers, Captain Harrison is ordered by Mr. Linarcos, the on board representative of the new owners, to go full steam ahead to Athens as any delay, which there have already been a few due to inclement weather, is costing the company money. With one of the dangers being the ship currently being top heavy and the Captain wanting to make an additional stop to pick up more cargo as ballast, the Poseidon, in the Mediterranean, hits disaster when, just after the stroke of midnight on New Year's morning with most of the passengers thus celebrating in the ballroom, it is struck by a massive wave the result of an undersea earthquake, the ship capsizing as a result. Of the survivors in the ballroom, Reverend Frank Scott, who has a complicated relationship with his faith, he en route to his new assignment of a poor parish in Africa meant for him to serve his penance, tries to convince the other survivors to follow him to try to make their way to the stern of the ship on what is now the highest level of the engine room, there where any rescue mission will probably occur in the hull being its thinnest, with time the essence due to the instability of ship's current situation, it which could shift and/or sink at any moment. He is only able to convince a handful of the others. Beyond the unknown dangers due to the ship's situation, the group, during their trek, has the further problem of the individual personalities, both in dealing with their situation and in the clashes between them, the most problematic in the latter category seemingly that between the strong willed reverend and the other alpha male, NYPD police detective Mike Rogo currently on a honeymoon with his ex-prostitute wife, Linda Rogo.