Lena was fourteen years old and knew the old library better than home. She lived by the river, in a town where the trains had long since stopped. Today, the library was housed in a former railway station, smelling of dust and old wood. Grandfather Anthony, a former cartographer, had left here a box of maps and a mysterious note. On the inside cover it said: Don't open if you don't know what you're looking for. Lena obviously wanted to know, so she opened the box, despite the rain outside the window. Inside lay a map of the city, unusual because it was drawn in double ink. Every street had a shadow, and the square in front of the station was crossed by a silver line. Beneath the line was the wind rose symbol and the date from fifty years ago. Lena called Mark, who was able to remove the padlocks without damage. They met after hours when the librarian closed the heavy door and the hall went out. The rain rumbled in the glass and they measured their steps according to their grandfather's notes. The wind rose on the map matched the mosaic in the middle of the former waiting room. As they set the map on the torch, the silver line overlapped with a crack in the terracotta. A chill blew from the crack, as if someone had opened a window on a cold morning. Marek knelt down and slid his fingers in, and a hidden mechanism hummed under the tile. The plate sprang open, revealing steps and a shaft that was not on the plans. A pale light came from below, blue, like the reflected moon in a puddle. They descended slowly, counting the steps, until they entered a circular chamber with an arch. The arch was of metal with the names of the winds and unknown signs carved on it. A sheet of air hung in the centre, trembling like thin skin on water. They heard a distant, dragging whistle, although the tracks had been gone for years. - 'Is this some kind of grandfather project? - whispered Marek, putting his hands in his pockets. - I don't know, but he wrote about windows that don't look out at the world. Lena held out her hand and the skin of the air bent under her finger. A scar in the shape of a small wind rose lit up on her wrist. The taffrail widened suddenly, showing a platform in the snow and another clock. The clock stood at twelve o'clock and the flakes hung in place. Someone on the other side turned slowly, as if sensing their gaze. - Leno? - rang out clearly from there, and the arch flashed, inviting and warning at the same time.