When a pretty Wren faints in a crowded train, Private Bud Flanagan and Captain Ches Allen are quick to render first aid. But over Bud's head, a heavy kitbag wobbles; it falls and scores a direct hit, knocking him unconscious. What follows is a dream sequence involving Ches, the Wren and Bud himself in a series of hilarious adventures as well as a magical medley of the duo's best-loved musical numbers!

Devon, 1815. In the dying days of the Napoleonic Wars, a Danish-American lieutenant, Cecil Stark, is captured attempting to run supplies to the French. Imprisoned at Dartmoor, he and his fellow captives make a desperate escape attempt, in which Stark is shot. He is found by Grace Malherb, and the two fall in love while he convalesces on her family estate. But Grace's father is heavily indebted to the boorish Peter Norcot, whose price for forgiving the loan is Grace's hand in marriage....

During a horrific storm at sea, the crew realizes that there is a murderer among them who is killing them off one by one.