Wren has followed the mysterious Omar Bakhoum from her home in Ysland across the frozen wastes of Europa to the warring cities of Constantia and Stamballa, where war is the least of Wren's problems. On steam-driven ironclads she meets more of Omar's immortal brethren who have all but lost their humanity, and in the icy streets she finds a legion of frozen corpses waging a war of their own against the living. While Omar leads the fight against the undead, Wren sets out alone to pit her wits and skills against the most powerful witch in the world, the immortal Rus crone Baba Yaga, who has gone mad with grief from the loss of her son, Koschei the Deathless. A cruel gauntlet awaits Wren as she confronts the spiteful souls of her dead teachers, her own secret fears made flesh, and the waking nightmares of Yaga herself. It's not all doom and gloom, though. A handsome young major in the Constantian army has caught Wren's eye, and Omar has taught her a few new tricks, like how to control the aether mists that reveal the souls of the dead. And if she can defeat the other-worldly forces besieging the city, the only thing left in her path will be a vast armada of naval destroyers and deadly airships. But that's all right. Wren likes a challenge.