An American officer, searching England for his dead brother's girlfriend, becomes involved in a jewel robbery.

American sailor David Martens, on shore leave in England, visits his brother Jack's grave. He meets fashion designer Sally Meadows, who by coincidence works with Jack's ex-fiancee, Diana, a model. Successful stylist Kingsley Beauchamp and financial backer Madame Dupont own the company where Sally and Diana are employed. Expensive jewels are to be worn by Diana when she models a new dress, but Beauchamp hires two men, Costard and Podd, to break into a safe after hours and steal the gems. Diana stumbles on the robbery and Costard kills her. He knocks David unconscious and decides to frame him for the theft, crashing a car with David inside, reporting it stolen and placing a ruby bracelet in David's pocket. While the police make David a prime suspect, Beauchamp and Costard dispose of Diana's body and the diamonds. They decide to murder David after he suspects them, using gas, but Sally saves him. Diana's body is found in a river. David goes to Beauchamp's home and discovers the missing dress worn by Diana. He knows that Beauchamp is about to fly to Amsterdam, so he hurries to the airport.