When two operatives go dark in Tampa, chasing the trail of an oligarch with ties to the demonic underworld, Vigilant Lock - the nation’s first and last line of defense against occult attack - sends their best to the rescue: Harmony Black, a troubled investigator and an elemental witch with a keen but tangled mind; and her partner Jessie Temple, the daughter of a supernatural slasher and the inheritor of her father’s powers.

The trail of clues leads them to the doorstep of Judah Cranston, a wealthy scientist with dark secrets and a darker agenda. Toss in an alluring marine biologist with eyes for Harmony, and a pair of demon-blooded troubleshooters on a hunt of their own, and Tampa Bay is heating up fast. As the mission takes Harmony and Jessie from the sun-drenched Florida coast to a gloomy New England fishing town steeped in forgotten history, they find themselves up against a threat far greater - and more otherworldly - than they ever expected.