Stanley Windrush (Ian Carmichael) is called up during WW2 and sent for training under the permanently exasperated Sergeant played by William Hartnell. Failing officer training he is sent to a holding camp presided over by Terry-Thomas, with his perpetual cry of "You're a shower, an absolute shower". Here he encounters the crafty Private Cox (Richard Attenborough) who explains to him how it is possible to avoid active service more or less indefinitely, only, as he explains "the trouble is you're educated, and that sort of limits, you, doesn't it?". Cox and his mates are up to all sorts of nefarious activities, and Windrush finds himself in all kinds of trouble. Meanwhile his dodgy Uncle Bertie (Dennis Price) is up to some shady dealings in art.
Finally Windrush's luck runs out and he is sent to train as a Japanese interpreter, but unfortunately he is sent to Germany, where Japanese isn't much use. He neds up disguised as a German officer, and once more encounters Uncle Bertie and Private Cox, who are intent on taking possession of as much as they can of a hoarde of art treasures stolen by the Nazis. Windrush, naturally, hasn't a clue what is going on, and manages to get himself captures by the British, who don't believe he's not a German. Safely back in England, with the war ended, it seems his troubles are over, but fate has more surprises in store for him.
This is a very funny film, with Richard Attenborough particularly good as crafty private Cox, and Terry-Thomas and Dennis Price very funny too. Ian Carmichael plays the bemused innocent in several films, but in my opinion this is by far most amusing.