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.