AllMovie

While traveling by train to a clandestine meeting with his married mistress, London stockbroker George (Roddy McDowall) befriends another passenger (Efrem Zimbalist Jr.). It soon develops that the other fellow is traveling to London for a rendezvous with his own married girlfriend -- and this isn't the only thing that the two men have in common. Once it is established that the stranger is also the husband of George's sweetheart, and that she had arranged this meeting in hopes that the stranger would murder George, a brand-new murder plan is hatched...or rather, two brand-new murder plans.