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.