The realtor called the staircase a "feature." It dropped past our new cellar, past a wine room nobody asked for, all the way down to a cold concrete floor. In Hollow Marsh, every house had one, each deeper than the last, like the town was competing. Our first night, Mrs. Edevane from next door knocked. "Whatever you do," she said, "don't go past the frost line."

I asked Mrs. Edevane what the frost line was. She pointed at my feet. "You'll feel it. The step where the air turns to ice. Below that, the house stops being yours." Then she left a thermos of soup and hurried home. I stood at the top of the stairs, looking down into the dark.

I dragged our heavy bookshelf to the top of the stairs and shoved it across the doorway. That night the tapping started anyway, but now it sounded angry. The bookshelf slid an inch toward me, then another, scraping across the floor. I leaned my whole weight against it and held on until sunrise. We never opened that door again. But every night it slides a little closer, and one night I won't be strong enough to hold it.