Oathbound by Tracy Deonn

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 with their Round Table fractured, leaderless, and missing its Kingsmage, as Selwyn has also disappeared. When Nick is detained by the Order’s Merlins, he invokes an ancient law that requires the High Council of Regents to convene at the Northern Keep and grant him an audience. No one knows what he will demand of them...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.