Maeb Langtofte is lucky to have a position in the household of the Earl of Pengraic—one of the most powerful men in England, whose holdings rival King Edmond's. She is lucky that his wife, Adelie, whom Maeb serves, is kind and pious (unlike the Earl, whom Maeb finds dark and secretive). But when word arrives that a plague is sweeping through Europe like a human wildfire, everyone in the Earl's household is put on edge. It is whispered that victims of this plague are spontaneously engulfed in flames—as if the flames of Hell had suddenly leapt up to claim them and the Devil himself is to blame.

As the disease spreads into England, so too does civil unrest. King Edmond calls his lords and their armies to return to London, and the Earl obeys, leaving Maeb and his family unprotected. It turns out that the Earl has been hiding more than state secrets, and that his family is at risk of losing not only their lives but also their souls. To her horror, Maeb will learn that the Devil himself may have arrived on her doorstep. And worse, what he demands may be running through her very veins.