A serial killer terrorizes London. Each victim is found with a telegram signed "The Marquis." There seems to be no other common thread between the victims, and Scotland Yard is baffled. Novelist and amateur sleuth, Paul Temple, is warned to stay away from the case, but he and his glamorous wife Steve can never refuse a good mystery.

The Goon Show hits the big screen. Professor Pure Heart absent-mindedly loses the top secret formula in Harry Jones' Grocery Shop. "Bats of the Yard", as Harry calls himself, finds it and attempts to return it to the Professor.