After a few minutes and several turns at intersections—the lights leading their way—the tunnel opened up into a room. Roots, as massive as tree trunks, steadied the rounded walls of earth. Here and there, the roots curled into smaller swirls of almost artful delicacy, a natural adornment. In the middle of the room lay a heap of furs and cushions—and on top of it, lounging in languorous predatory ease, loomed a giant black wolf, almost twice the size of a normal canine.

Marga stopped dead, her muscles locked in place, her heart pounding with the rush of fear. “Atticus,” she called out mentally, “please tell me Lucas has ordered that...