Lorcas Fellken is thirteen when his father gives him a rock for a birthday present. But not just any rock - this one is the cornerstone to an ancient castle. Years later, Lorcas moves to his family’s summerhouse and begins reconstructing the castle, one stone at a time. Egged on by a shadow that lives under the stone, he adds layer after layer. But as he builds, the castle becomes more aware - and more malevolent. Lorcas slowly creates something he never imagined, despite the efforts of a mysterious group bent on keeping the castle from being rebuilt. Along the way, he gains surprising powers - for a price. Would the castle have been better left in ruins?

Following the destruction of the castle by the Knights, Rook seems to have disappeared underground. But Lorcas, Zumar, and Tomash discover that there are big plans afoot, and the future of one or all of them may be in danger. Meanwhile, the Knights set their own, devastating plan in action. If it succeeds, Rook may be disabled for generations or even destroyed. If it fails, the Knights risk increasing the Fell Ken’s power astronomically. Just how sneaky has Rook been – and what will he do to save himself?