The Daily Clarion hires detective story writer Steve Colt to investigate the deaths of a group of scientists working on an atomic rocket development project. Behind the killings is fortune teller Sombra, a spy from an Asian country intent on world domination, who is determined to pilfer the atomic rocket by luring workers from the project to her parlor and killing them with black widow spider venom when they refuse to cooperate.

A soldier, returning home from war, chances upon a stranger who offers to buy his violin. The stranger is none other than the devil.

Inspector Cassin, a renowned Paris detective, departs to the country for a much-needed break. There he falls in love with the innkeeper’s daughter, Nanette, who is already betrothed to a local farmer. On the evening of their engagement party, Nanette and the farmer both disappear. Cassin takes up the case immediately to discover what happened to them and who is responsible.