Monica Rhodes is a bounty hunter. Although an uncommon profession for a woman, she excels at her work and enjoys the solitude it brings. In St. Louis, she accepts a bounty on an Englishman who is accused of murder, witchcraft, devil-worship, and worse. Along the way, she meets Ruprecht Eichen, a German doctor seeking revenge for his murdered family members. The two strike up a cautious partnership in pursuit of their mutual foe, but Monica can't help but wonder whether simple revenge is all that motivates him. Whatever the answer, it is clear that they must rely on one another; a black moon is rising over the last days of the Old West, bringing with it terror, mystery, and intrigue.