Life for Peg Bowman is rough in the infamous slums of Five Points, New York, but her brother's murder changes everything.
Thrust into incredible worlds beyond any story she's ever heard, Peg meets Sir Godfrey, an eleven-hundred-year-old knight from Charlemagne's court, trainer of Paladins. He reveals to Peg her family's ancient obligation to protect the Key of Apollyon, a relic of immense power. She is the last descendant of the Paladins and his only hope for keeping it safe.
When Godfrey confides her brother was murdered because of the Key, Peg rejects her calling and demands revenge, a luxury she can ill afford as otherworldly creatures seek her death to claim the key's power for themselves.
Can Godfrey and his faithful retinue-Chim the Hobgoblin, Rebecca the Jewish maven and healer, and Jack the sometimes human and sometimes seven-foot black dog-keep her safe and convince her that her calling is worth pursuing? Or will she succumb to the key's lure and wield it for revenge?