American Frank Pryor (Lloyd Bridges) arrives in London to pick up the threads of a wartime romance. As he disembarks, fellow passenger Kendall Brown is assassinated and Pryor finds himself caught up in a murder inquiry. The victim was killed by a mysterious sniper, known as the 'limping man'. Pryor's wartime amour is actress Pauline French (Moira Lister) who he hasn't seen in six years. She happens to be a crack shot with a rifle, and the dead man had a picture of her in his possession... Scotland Yard Detective Cameron (Leslie Phillips) is assigned to the case, and Pryor and his sweetheart become his chief suspects.