In this spoof western, Judge Burke (Kenneth Williams) is convinced that Marshall P Knutt (Jim Dale) is the lawman who will rid him of the Rumpo Kid (Sid James) and his band of desperados. But to a sanitary engineer such as Knutt, cleaning up Stodge City has a totally different meaning and the round-up is left to straight shooting Annie Oakley (Angela Douglas). Shot in the untamed wilds of Pinewood Studios, the 11th Carry On finds the team in mid-season form. All the regulars impress, but Charles Hawtrey steals the picture as the firewater-swilling Chief Big Heap.

Stodge City is in the grip of the Rumpo Kid and his gang. Mistaken identity again takes a hand as a 'sanitary engineer' named Marshal P. Knutt is mistaken for a law marshal. Being the conscientious sort, Marshal tries to help the town get rid of Rumpo, and a showdown is inevitable. Marshal has two aids—revenge-seeking Annie Oakley and his sanitary expertise.