A year after losing his job retrieving overdue occult books and collecting fines for the LeFleur family library, Martin Abueg finds himself embroiled in library business again when Lucifer's sister, Lady Priscilla, sends a hellhound to New Orleans to find a missing abracadabbler and a supernatural object called Abaddon's Key.

Meanwhile, in Chicago, a suspicious fire destroys the city's premiere occult library, Orchard Hall, leaving two unidentified bodies in its ruins and a comatose survivor who's been secretly searching for an angel trapped inside a human being.

When head librarian, Almaz Cavassa, hires Martin to investigate the fire and retrieve Abaddon's Key before Hell does, he finds himself sinking deeper into the consequences of his murderous past and uncovers a devil's bargain involving a dead librarian that will upend Hell's civil war and unleash chaos into The Dark Easy.