Another world exists beyond the one that humans can see-a world populated by demons. For centuries, demons have crossed into our world, some looking for a new life, adventure, or just a job. But many are intent on causing chaos and destruction, feasting on human flesh and fear. A tenuous Peace Treaty is the only barrier between the worlds, the only thing protecting humankind from utter devastation.

Every hundred years the Treaty must be renewed--and the time for that secret ceremony is at hand. Violent demonic splinter factions that are hell-bent on destroying the ancient pact are preparing to assassinate a key figure who is vital to the signing ceremony.

Enter the Black Guard, a secret police force that protects the boundary between the dark world and our own. It's the job of two Black Guard agents--Makie, a gorgeous demon, and Taki, a hard-boiled human--to form an unlikely partnership, stop the assassination, and avert an all-out war. But to save both their worlds, they must risk not only their lives, but their very souls!