Mistwood by Leah Cypess

The Shifter is an immortal creature bound by an ancient spell to protect the kings of Samorna. When the realm is peaceful, she retreats to the Mistwood.But when she is needed she always comes.

Isabel remembers nothing. Nothing before the prince rode into her forest to take her back to the castle. Nothing about who she is supposed to be, or the powers she is supposed to have.

Prince Rokan needs Isabel to be his Shifter. He needs her ability to shift to animal form, to wind, to mist. He needs her lethal speed and superhuman strength. And he needs her loyalty—because without it, she may be his greatest threat.

Isabel knows that her prince is lying to her, but she can't help wanting to protect him from the dangers and intrigues of the court . . . until a deadly truth shatters the bond between them.

Now Isabel faces a choice that threatens her loyalty, her heart . . . and everything she thought she knew.