It's war time London and the Crazy Gang (Flanagan & Allen, Nervo & Knox, Naughton & Gold) are doing their bit for the war effort by running a fish and chip stall using their platoon's barrage balloon for advertising. Their Sgt Major is not happy about this and orders them to take the balloon down, but a freak heavy wind accidentally carries the gang away to Nazi Germany. They are captured and placed in a detention camp where they meet an elderly prisoner named Jerry, who possess a map for the location of a secret weapon which will win the war! Fortunately Teddy Knox's impersonation of Hitler lands him the spot of pretending to be the Fuhrer at a gala dinner and the gang are allowed out of the camp. However the Nazis have other ideas for their substitute leader.

In the years after his graduation Allen Shepherd has become a successful novelist and has married Jane Anderson. A firm proponent of traditional sex roles, Shepherd leaves Jane when she accepts a teaching post at Oxford. He later changes his views, and the couple is reunited.