While at his dying wife's bedside, Louis Darque, a recently promoted detective, is confronted by his absentee biological father, a demon named B'lial. The demon offers Louis the chance to save the life of his wife if he 'works' for him on earth. He informs him that because of his mixed blood he has certain demonic traits, such as immortality and the ability to travel to and from Hell. While Louis attempts to solve a series of murders on Earth and battles in Hell, he finds he has a twin brother: Obscure. In an effort to save the world from their father, and so Louis can have peace and Obscure the missing darkness he so craves, the two team up to fight B'lial on his own turf.....and Hell makes it clear that Louis is certainly not welcome there....