Advertised as a pure-and-simple horror film, Soul of a Monster is actually an adroit variation on the "Faust" legend. George Macready plays Dr. George Winson, who is saved from the brink of death by the intervention of his loving wife Ann (Jeanne Bates). In desperation, Ann had offered to make a deal with the devil to keep her husband alive, whereupon an emissary of Satan, a hypnotist named Lilyan Gregg (Rose Hobart) made an appearance. Upon his recovery, the previously kind-hearted Winson turns evil, doing the Devil's work while under Lilyan's diabolical spell. But Ann and her friends are not susceptible to Lilyan's mesmerizing prowess, enabling them to launch a counteroffensive against the Dark Prince.