Harry Compton, a naive young man, is dismissed by the bank in which he worked. Desperately in need of a job, he agrees to become a Soviet spy. Assigned with the mission to steal the "Avalanche" secret file from Sir Dumfrey, he gets to know Penny, a ravishing but somewhat dumb dressmaker. The young woman spontaneously offers to help Harry in his actions. But they are pursued by bad luck. What's more, they keep accumulating blunders. To make matters worse, the MI6 has learned of the operation...