Fourteen-year-old Lena spent the summer in the library where her mother worked. She cleaned the covers, organised the files and looked into the nooks and crannies of the storeroom. It smelled of dust, old glue and lemon soap from the duty room. The library was like a labyrinth, full of semicircles, steps and blind corridors. Lena carried a sketchbook because she wanted to stop everything with line and shadow. Her imagination helped her when the world looked too flat, even in summer. One afternoon she found a thin linen book without title or signature. There was a single sentence on the linen cover: the drawing is the map, the map is the door. Inside lay a graphite pencil and most of the pages were blank. Lena drew a simple plan of her street, adding a door between numbers ten and twelve. The paper warmed slightly and a translucent streak shimmered in the air. Lena snorted with laughter, closed the book and tucked it under her sweatshirt. In the evening, she walked between the tenement houses numbered ten and twelve as if nothing had happened. Between the facades stood a narrow door with a black handle that had not been there before. She took a picture, but all that appeared on the screen was a smooth wall. - Maks, can you see it? - she wrote, sending him the photo and the exact address. He wrote back after a while: There is no door there, seriously, Lena. She touched the stone; it was cold, as if something was pulling the heat from her fingertips. On the board above the handle she saw the mark from the book's liner, a thin crescent moon. The next day she returned to the reading room as the rain pounded against the windows like fingers. On a blank page she drew a plan of the library with a hidden floor, named Floor Zero. She drew a door behind bookcase A12, between the ground floor and the basement, seemingly a thin gap. The book vibrated, the light bulb flicked, and something crunched like old wood in the silence. She moved the volumes on shelf A12 and felt a chill that was not library-like. A vertical crevice waited behind the books; it smelled of rain and wet chalk, though dry all around. Then she heard footsteps, steady and unfamiliar, and someone whispering: Lena... She reached out her hand to the door handle as the metal on the other side moved first.