Penfold has been kidnapped by Baron Greenback, who forces Dangermouse to gather together four ingredients of an ancient spell for creating an invincible monster. They are: four hairs from a Yeti, a twig from a Witches Broom, a piece of the dreaded Fog Monster of old London town and two feathers from a vampire duck. In the middle of all this, another mission comes up, this one to buy a washing machine on sale for the PM's missus.