Mira was nineteen and on night duty at the Cartography Museum, where dust piled up like a silent sea on the display cases. She catalogued maps, looked through labels, swept the extinguished lights in the study with a ruler. Her grandmother was a cartographer who wrote letters in pine resin-scented ink and left her a brass key with a note: "Don't open the wind if you can't close it". Mira wore the key on a string under her sweatshirt, more out of habit than belief in warnings. Outside the window, the rain was slamming down and the wind scattered the street lights into thick streaks. In the main room stood a huge map of the Unwritten Archipelago, donated to the museum without description or date. A barely visible crack glinted in the corner of the cartouche, as if someone had lost a piece of the sigil. Mira pulled off her gloves, touched the frame and felt a tiny tremor that had nothing to do with the storm. She took out the key, aligning its teeth with the slot. They fitted as if they had been waiting for years. As she turned, the lines of length and breadth darkened, then floated over the parchment like the veins of a glassy fish. There was a cool breeze from the map, a smell of salt and freshly cut paper. - Mrs Miro? - rang out from the corridor. - We close in a quarter of an hour. She nodded, though no one could see her, and did not let go of the key. It began to whisper something she couldn't find in the catalogues: a repetitive hum, arranged into syllables by parallel currents. A clearance opened in the frame, not glass and not water, but made of movement. Behind it, dunes of paper rippled, lantern needles flashed along the spines of books, and a river of ink flowed uphill. A comma-like butterfly flew out of the clearance; it settled on her hand and left a dot that wouldn't budge. - Who is waking up the passage there? - sounded from within, as if a room full of maps was speaking. A boy in a coat lined with tabs and with a cracked astrolabe emerged from the shadows. His hair was tousled with wind that smelled of ink. - 'We're looking for the Guardian of the North,' he said, looking straight at the key. - Without it, the corridors will close and the routes will fade from memory. I've seen the trails slammed shut, and I don't want to be left in silence. - Is this a joke? - whispered Mira, not sounding convinced. At the same moment the locking alarm sounded and the light at the door blinked red. - Miss Mira, we're leaving! - called out the caretaker, closer than before. A streak of wind slipped out through the frame of the map and snatched her badge, which disappeared into that side like a swallowed bookmark. - This entrance won't last long,' the boy warned. - The waves of paper are not waiting. Will you go? The needle in the astrolabe twisted wildly; it came into focus, pointed in a direction, and something from within grabbed Mira's wrist.