Humble stamp dealer Otto Becker has little to do with international politics, so when he receives a surprise visit from his estranged twin brother and Nazi spy, Baron Hugo von Detner, his world is thrown into turmoil. Threatening Becker with deportation, Hugo forces him to use his shop as a front for espionage.
Bob Stevens awakens in a hospital with a gunshot wound to his head, and is told that he has been in Paris for ten days. However, this cannot be true because he insists that he crashed his plane and has no recollection of being anywhere for ten days. Bob decides to follow a note found in his jacket, to the woman who wrote it, "Miss D", and get to the bottom of the whole strange situation.
A London cat burglar falls for the girlfriend of a stockbroker who used to be his partner.
