The key to a flat in wartime Britain may augur bad luck for a succession of tug captains of the Royal Navy whose task is to rescue crippled ships in "U-boat Alley."

As each takes possession from his unfortunate predecessor, the flat's other occupant, a Swiss expatriate named Stella, apparently comes with it.

American David Ross (William Holden), a former tugboat captain now in the Canadian Army, is hastily commissioned in the Royal Navy and assigned to rotating command of W88, a double-screwed rescue tug then in dry dock due to battle damage.

The slow, poorly armed tugs bring in "lame ducks," freighters crippled near Britain by German attacks.

David is reunited with an old friend, Captain Chris Ford (Trevor Howard), who commands another tug about to go on a mission.

That night Chris brings him home to his flat to meet his lover, Stella (Sophia Loren), who wears a wedding ring.

Knowing the extreme danger of his job, Van Barger then gave a copy of his key to the flat to Chris, so that Stella would be taken care of no matter what.

In the other, purportedly filmed to satisfy the American Motion Picture Production Code by showing that David and Stella pay for their sexual relationship, he just misses catching it, but insists he will search for and find her.

[4] However a published history of British films subjected to PCA scrutiny before their American release presents a slightly different version.

The casting of Holden and Loren necessitated script rationales for their presence in 1941 England, but the appointment of an American in the RNVR as a ship's captain during the early years of World War II was historically possible.