A recently married heiress, Ruth Stanton (Jeanne Crain), embarks on a honeymoon cruise with her new husband, John Bowman (Carl Betz). However, shortly after getting on board, John disappears. None of the crew remember seeing him, and the ship's manifest has Ruth registered alone and under her maiden name. Ruth wanders the boat in search of John, but soon the captain and crew believe Ruth must be crazy. Only kindly Dr. Manning (Michael Rennie) takes her seriously and helps unravel the mystery.