David Ross (William Holden) is a Canadian sergeant brought to England for a perilous mission: to captain a tugboat responsible for bringing in crippled ships damaged by German torpedoes. Assisted by old friend and fellow captain Chris Ford (Trevor Howard), David is taught the ropes and offered a key to an apartment shared by Stella (Sophia Loren). When David finds out that the previous men who had this key all died at sea, he is reluctant to accept. When he does, David and Stella fall in love, but will David fall prey to the curse bestowed upon the others?