Scilla and her boss Eva are two German spies who travel to London in order to steal the plans for a special new tank. Under the false name of Ilde Tabor, Scilla seduces engineer Dorian Baker, the keeper of the plans, and then drugs him. However, he snaps out of it quicker than Scilla had anticipated, leading her to take his pistol and kill him.
Protagonist Wallestein - who is actually a swamp monster that wears the mask of a deceased count and works with the authorities - manages to track the two down inside of a deserted looking house, where they are caught making love. When the monster enters, the alarmed Eva attempts to grab her pistol from a nearby drawer. Wallestein beats her to it, however, and severs her hand completely from her arm and then kills her by bashing her head into the wall. He then chokes Scilla to death and retrieves the stolen plans.