John Gielgud charmingly portrays the novelist-cum-officer dragooned by the British spy service into travelling to Switzerland on the trail of a Nazi spy. He is assigned two assistants - a rather naive, but keen, Madeleine Carroll "Elsa" and a suitable sleazy, but lethal, Peter Lorre "as The General". Their first attempt to fulfil their mission goes awry somewhat, as they dispatch the wrong person. It is at this point their consciences start to kick in and they question the morals of their mission - particularly when they actually do discover the identity of the enemy secret agent. Hitchcock and Charles Bennett adapt the Somerset Maugham story with plenty of attention to the detail and the characterisation; the direction is taut and the suspense on the train towards the end keep this enthralling.