The hum did not stop when the Custodian left. If anything it grew steadier once his presence was gone from the room, a low resonant note that seemed to come from somewhere inside Sera and Luna both rather than from their throats, felt more than heard, the kind of sound that settled into the bones of everyone standing close enough to feel it.

Marina had never been more afraid of something so quiet.

"Sera," she said, keeping her voice as level as she could manage with her daughter still trembling against her chest. "Sweetheart, can you hear that?"

Sera nodded against her shoulder. "It's always there," she whispered. "It got...