Training Sgt. Grimshawe accepts a bet that his last platoon of National Servicemen before he retires will pass out as Star Squad. His hopes are dashed when he meets the recruits. As training proceeds each recruit makes his own contribution to the chaos, but on the eve of the passing-out parade, impressed by Grimshawe's relatively gentle methods, they decide to retrieve their reputation. To their own and the Sergeant's surprise they win the Star Squad award.
The professional skill of William Hartnell and Dora Bryan lends some reality and humour to this conventional farce, in which all the characters come from stock. Carry On, Sergeant is a traditionally English mixture of old farcical situations, well-worn jokes, and comic postcard characters. Charles Hawtrey, as a weedy incompetent, and Kenneth Williams, as a condescending intellectual, provide some genuine laughs. The rest of the humour is either overdone or half-baked.