The Demon's Surrender — Sarah Rees Brennan

The Goblin Market, where lives are won and lost and magic is bought and sold, has always been the center of Sin's world. Now the war between the magicians and the Market is escalating, and her position as future leader is threatened by a rival. Sin knows Mae can never really take control of the Market: Mae is a tourist, and her brother, Jamie, is not only a powerful magician. but also the Aventurine Circle's newest and deadliest weapon. But as the Market gains strange new allies, support for Mae is growing, and Sin's only chance to lead is to accomplish an impossible task.

Among the most dangerous of the Market's allies are the enigmatic Ryves brothers. Nick was once more than Sin's friend, but she cannot forget his demonic nature. Alan has always been Sin's enemy, and she now owes him a debt she cannot repay. Even as the unlikely allies discover common ground and new feelings arise among them, Sin realizes the brothers pose a greater danger than she dreamed. Alan is marked -- and being tortured -- by the magicians, and Nick may be working for them.

When Sin's family secrets are revealed and betrayal comes from someone they trusted, a terrible sacrifice has to be made if anyone is going to survive the final battle.

The demon's surrender could destroy them all.