Bela Lugosi is a mysterious figure known as “The Vampire” who comes to England to complete experiments in a mad bid to control the world.
He can only achieve his ambition with the assistance of a radar-controlled Robot secretly shipped to him. Unfortunately, the crate containing the Robot, is delivered by mistake to Mother Riley. Through radar control, the Vampire makes contact with his Robot and orders it to transport itself and Mother Riley to his house.
The Vampire holds Mother Riley captive. Riley, turning detective, discovers the Vampire is up to no good. When the latter leaves for the dockyards to visit a ship, Riley rolls up her sleeves and goes into a whirlwind of action to frustrate the Vampire’s plans. The old lady wins in the end, even though her methods are somewhat unconventional, and the film climaxes in a blaze of side-splitting slapstick.