Arthur White lived a simple life tending the dead in a quiet cemetery, until meeting a mysterious stranger known only as Mr. Black. In a few short hours, the stranger turns the groundskeeper's life upside down, burdening Arthur with an immortal clockwork heart.
Over the course of years, Arthur works as Mr. Black's right hand, doing the things the old warlock cannot dirty his hands with. The death of a mutual friend and the discovery of Lucifer's cast-off heart catalyze them into action, setting off a global chase to recover the artifact and open the door to death.
Along the way, Arthur struggles with evils he's committed, dreams of loss that plague him, and desperate loneliness that may be cured by the appearance of a mysterious new companion, Ava. But before they can get to know one another, they must confront a cult out to steal the heart for their own ends.
Before it's over, Arthur, Ava, and Mr. Black will have to face who they are and what they've done, or perish in a brutal new world. Whatever remains from the ashes may be their only hope.