Based on the novels of W. Somerset Maugham, The Secret Agent is the second in a trilogy of Alfred Hitchcock spy movies (along with The 39 Steps and Sabotage). Set during WWI, John Gielgud plays British novelist Edgar Brodie who discovers that a government agency has faked his own death. He is then given orders to go to Switzerland to kill a German agent.
He goes by the name of Richard Ashenden and travels with secret agent Elsa Carrington (Madeleine Carroll), who poses as his wife. Richard joins professional killer the General (Peter Lorre) to look for clues, which leads them to suspect the tourist Caypor (Percy Marmont).
Elsa occupies Caypor's wife, Florence Kahn, while Richard and the General attempt to complete their mission during a climbing trip in the Alps. It turns out he was the wrong man, so the spies reluctantly start another search for clues that leads them to the American charmer Robert Marvin (Robert Young).
Unfortunately, he has just boarded a train to Greece with Elsa, so they have to get onboard and warn her. The situation is complicated with an air attack, where several key players meet their fate. The Secret Agent marked a rare instance where Hitchcock was pressured into changing the ending from the more grim original.