Oathbound by Tracy Deonn

Tracy Deonn’s #1 bestselling Legendborn Cycle continues in the sensational third book about a dazzling contemporary fantasy world that blends Southern Black Girl Magic with secret societies and the legend of King Arthur!

Severed from the Legendborn. Oathbound to a monster.
Bree Matthews is alone. She exiled herself from the Legendborn Order, cut her ancestral connections, and turned away from the friends who can’t understand the impossible cost of her powers. This is the only way to keep herself—and those she loves—safe.
But Bree’s decision has come with a terrible price: an unbreakable bargain with the Shadow King himself, a shapeshifter who can move between humanity, the demon underworld, and the Legendborn secret society. In exchange for training to wield her unprecedented abilities, Bree has put her future in the Shadow King’s hands—and unwittingly bound herself to do his bidding as his new protégé.
Meanwhile, the other Scions must face war while their Round Table is fractured, leaderless, and missing its Kingsmage, as Selwyn has also disappeared. When Nick invokes an ancient law that requires the High Council of Regents to grant him an audience, the Order’s Merlins imprison him. No one knows what he will demand of the Regents…or what secrets he has kept hidden from the Table.

As a string of mysterious kidnappings escalates and Merlins are found dead, it becomes clear that no matter how hard Bree runs from who she is, the past will always find her.