"A place," Mara said. "A hollow is a hole made by time. Or maybe by people."

At first glance it was nothing: a wooden chest roughly the size of a shoebox, scored with six shallow, deliberate knots arranged in a tight circle on the top. The knots were bound by a faded red thread that had been knotted six times, each knot tight and precise, as if someone had taken time to count them and then counted again. There was no lock. A small curling label, brittle as old parchment, read only: Return to the hollow.

"Where did you get it?" he asked once, eyes bright.