(1) Nine people explore a cruise ship at sea in a manner that turns their whole lives upside down. (2) A passenger ship, on her way to the scrap yard is pushed to her limits by the new owners to save on the dismantling fees. A tidal wave hits her, flipping her over so that all the internal rooms are upside down. A priest takes a mixed band of survivors on a journey through the bowels of the ship in an attempt to survive. (3) At midnight on New Year's Eve, the SS Poseidon is struck by a 90-foot tidal wave and is capsized. 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 upside-down ship to reach the bottom (the propeller shaft), now the top.