At midnight on New Years Eve the S.S. Poseidon is struck by a 90′ tidal wave and is capsized. The Reverend Frank Scott leads nine Survivors; an elderly couple, Manny and Belle Rosen headed to Israel to see their grandson; A New York detective and his ex-prostitute wife, Mike and Linda Rogo on their second honeymoon to Italy; A young brother and sister, Robin and Susan Shelby going to meet their parents in Greece; A haberdasher James Martin; a pop singer Nonnie Parry, and a waiter from the ship Acres. They travel from the grand ballroom struggling through, steam, fire and rising water in the up-side-down ship to reach the bottom (the propeller shaft), now the top.

Annie and her policeman boyfriend Alex decide to take a romantic ocean cruise together. Once at sea, however, one of the passengers, a disgruntled computer genius named Giger, disables the ship. Alex must now foil Giger’s plans and bring everyone back safely to shore, but how can he outwit a man who can control the entire ship from his keyboard?