Charting the military escapades of serial bungler Tommy Josser, Josser in the Army sees the hapless hero in France during wartime, where he masquerades as a German general, unmasks a spy, gets captured and then makes a spectacular airborne escape!

Bumbling policeman P.C. Josser is dismissed from the force after a disastrous attempt to distinguish himself at a nightclub. Mistaking his own comrades for criminals, he inadvertently "bowls them over like nine-pins," leading to his immediate firing. After losing his job, Josser sets himself up as a private detective. He is hired by a young lady who owns a racehorse and needs protection for her "favourite" horse before a big race. To protect the animal, Josser goes undercover as a stableman. Despite his efforts, the horse is drugged, leading to further comedic mishaps as he attempts to solve the case and redeem his reputation.

'Hall porter forced to join Navy while tracking spies.' (British Film Catalogue)

The fumble fingered Josser finds himself thrown off the police force for his constant bungling, but by the picture's end, he manages to redeem himself by breaking up a ring of crooks who have been fixing horse-races by doping up the horses.