July, 1917. DI Ernest Hardcastle and his assistant, DS Charles Marriott, investigate the murder of a cashier operating in London's Victoria Station. An army officer claims to have seen the murderer running away, and an army cap left behind appears to identify the criminal. Hardcastle believes that it will be a simple matter to go to Aldershot and arrest him, but things are never as easy as they seem. Soon Hardcastle and Marriott find themselves investigating a frustrating and seemingly unsolvable case. Has Hardcastle finally met his match? . . .