It's 1935. The air is already thick with anticipation of the coming war. But in the outskirts of Prague, in a medieval castle, an equally evil slumbers. It houses the 'Devil's Six'—murderers renowned for their cruelty. A young psychiatrist, a student of the legendary Carl Jung, Viktor Kosarek, arrives at the asylum in hopes of uncovering the nature of evil and discovering the devil's aspect in these patients. Meanwhile, Prague is shaken by a series of brutal murders committed by a serial killer known as 'Leather Apron.' Viktor tries to connect the doomed murders to the dark secrets of his patients. But perhaps the devil himself is involved...