Outlaw Johnny Finger, better known as The Rumpo Kid (Sid James), rides into the frontier town of Stodge City, and immediately guns down three complete strangers, orders alcohol at the saloon—horrifying Judge Burke (Kenneth Williams), the teetotal Mayor of Stodge City—and kills the town's sheriff, Albert Earp (Jon Pertwee).

Rumpo then takes over the saloon, courting its former owner, the sharp-shooting Belle (Joan Sims), and turns the town into a base for thieves and cattle-rustlers.

In Washington DC, English "sanitation engineer first class" Marshal P. Knutt (Jim Dale) arrives in America in the hope of revolutionizing the American sewerage system.

He accidentally walks into the office of the Commissioner, thinking it to be the Public Works Department, and is mistaken for a US Peace Marshal, and is promptly sent out to Stodge City.

Writing in 1966, The Monthly Film Bulletin opined "there are some quite clever and amusing ideas, but an even heavier than usual reliance on outrageous puns and not particularly subtle double entendres.