Humans are dying in San Francisco. The most shunned angel on Earth may very well hold the key as to why...

When Cassius Black moves to San Francisco for a fresh start, the angel's hopes of staying below the radar of the supernatural organizations that oversee the otherworldly and magic users in the city are dashed when he stumbles across a dead body in the sewers. His grim discovery soon puts him in the sights of the Argonaut Agency and Francis Strickland, the bureau director who knows his darkest secrets.

Morgan King and his team of Argonaut agents have been on the hunt all summer for the culprits behind a series of gruesome killings that have rocked the city. Killings that bear sinister hallmarks of human sacrificial rituals where the victims' souls have been stolen. When Fate puts Cassius in Morgan's path, he realizes the angel everyone likes to call The Devil may very well be the only person who can help them track down the murderers.

Morgan and Cassius soon find themselves chasing down a sect of black-magic sorcerers and crossing paths with a mysterious warlock whose actions evoke disturbing echoes of an incident from Cassius's past. As rumors of a potential plot to tear open the Nether reach their ears, Cassius and Morgan must work together to defeat their common enemy and save the city from destruction, all while fighting their growing attraction for one another.