Stanley Windrush has to interrupt his university education when he is called up towards the end of the war. He quickly proves himself not to be officer material, but befriends wily Private Percival Cox who knows exactly how all the scams work in the confused world of the British Army. And Stanley's brigadier War Office uncle seems to be up to something more than a bit shady too - and they are both soon working for him, behind the enemy lines.

General Candy, who's overseeing an English squad in 1943, is a veteran leader who doesn't have the respect of the men he's training and is considered out-of-touch with what's needed to win the war. But it wasn't always this way. Flashing back to his early career in the Boer War and World War I, we see a dashing young officer whose life has been shaped by three different women, and by a lasting friendship with a German soldier.

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.