This trade paperback collects the first adventures of Mercy Sparx (#0-4).
Mercy Sparx is a devil girl going about her regular mundane life in the strange land of Sheol (a place between Heaven, Hell & Purgatory where the misfits of the divine fall through the cracks) which usually entails getting drunk too often and causing a lot of trouble. That is until one day when a mysterious and powerful demon abducts her on orders from Heaven that she is to live amongst us on Earth, hunting angels that have abandoned their stations.
Heaven gives Mercy a human disguise, the means to hunt the angels down, a crappy apartment and a paycheck every two weeks. And she finds a cool heavy metal loving roommate to share rent with, who happens to be a genius with skills that come in handy for her mission.