Fog was descending on the Bay harbour as Kaja returned from school. Her grandfather's shortwave radio, quiet for years, suddenly beeped in her backpack. A broken rhythm erupted from the speaker: three short, three long, three short. Behind her back, the lighthouse, closed for renovation, had been extinguished for months. In the town everyone knew that the lighthouse should not emit anything. Her grandfather had taught her to listen to the waves, but had never mentioned signals. But that night she saw one pale flash from the kitchen window. Olek came in after nine o'clock, still in his jacket, with a map of the bay under his arm. In the margins he had marked buoys and the old harbour railway tracks. They listened to a gruff squeak that returned every five minutes, always identical. - 'That's no ordinary noise,' muttered Olek. - Someone is broadcasting from the lighthouse. Kaja pulled out the old wicket-key the caretaker sometimes frequented her with. They went to the sea, as the fog became lighter and the waves were silent. In the museum courtyard lay a coiled rope, wet as a snake, and an open window. Inside the keeper's desk they found a notebook stamped: Inventory - Lighthouse. The pages smelled of salt, and between the entries someone had annotated nervously in pencil. There were words about sounds in the tunnel, one step too many and shadows. At the end was yesterday's sentence: if he returns, broadcast SOS continuously. Taped to the back cover was a brass key, heavier than it looked. Under the stairs they found a metal hatch with a padlock, hidden under a box of lamps. The key fitted, and the hinge beeped as quietly as if someone was listening. Behind the flap went down winding steps, cool and damp from the fog. Kaja slipped the walkie-talkie into her pocket and immediately felt a crackle. - Hello? - she whispered. - If it's a joke, stop, will you? The speaker sizzled and boomed out a noise in which her name formed. Kaja froze and Olek raised his torch, illuminating the black throat of the stairs. Then they heard a small clatter against metal, as if someone had placed a shoe on the step. The radio buzzed once more and said clearly: Don't turn around.