As the captain of an unarmed tugboat assigned to rescue Allied ships that have been disabled by the German Navy, David Ross (William Holden) is repeatedly placed in grave danger. Before dying in the line of duty, fellow captain Chris Ford (Trevor Howard) gives Ross the key to an apartment occupied by a lovely and caring Swiss-Italian immigrant named Stella (Sophia Loren). Though Ross discovers that he is just the next in a long line of rescue boat captains she has comforted up until the time of their deaths, he cannot help falling in love - even when he begins to suspect that his life will be the next one lost in another daring wartime rescue.