John Jaspers is a mental patient who has become the lover of his female psychiatrist, Jade de Camp. After disappearing from the asylum, Jaspers somehow sells his soul the devil, in the guise of a criminal mastermind known as M (as for Mephistopheles). He is then changed into a costume-clad, super-strong vigilante, armed with seemingly unbreakable, razor-sharp metal claws. Jaspers eventually becomes too uncontrollable for M and starts preying upon New York City's underworld that M partly controls.