Asher Grey is Victorian London's only consulting exorcist. Beneath the surface of the physical world is the realm of the mystical and unnatural-the things that go bump in the night. Sorting these things out is Asher's calling. If only he could manage to get a paying client or two.

When Asher is called to perform an exorcism on an asylum patient, he quickly realizes this is not a typical case; the thing possessing the patient threatens the imminent arrival of a dark entity. Suddenly, Asher's childhood friend appears and interjects herself into the case, putting her at risk.

All Asher wants is to stop the arrival of the fiend and to keep his friend from harm-but doing both may not be possible.