Captain Casey Abbott (Ronald Reagan) commands an American submarine in the Pacific during World War II. When a perilous mission to retrieve a new Japanese mine for study goes awry, he's forced to abandon a likable combat diver, Wes Barton (Harry Lauter). Abbott's orders to leave a man behind appear to be justified, but his second in command, Don Landon (Arthur Franz), believes he had ulterior motives: Barton had been competing for the attention of his love interest, Helen (Nancy Davis).