By stopping the shipments of slaves to the neighboring kingdom of Mortmesne, Kelsea has crossed the brutal Red Queen, who derives her power from dark magic and who is sending her fearsome army into the Tearling to take what she claims is hers. And nothing can stop the invasion.

But as the Mort army draws ever closer, Kelsea develops a mysterious connection to a time before the Crossing. She finds herself relying on a strange and possibly dangerous ally: a woman named Lily, fighting for her life in a world where being female can feel like a crime. Soon Kelsea herself begins to change; she does not recognize either her reflection in the mirror or the extraordinary power she now commands. The fate of the Tearling—and that of Kelsea's own soul—may rest with Lily and her story, but Queen Kelsea is running out of time.