Lena stayed after lessons because she missed the bus and the physics test. The empty corridor sounded different when the school bell wasn't counting down. Water dripped from the ceiling and something hummed quietly under the physics room. Lena crouched by a cracked tile and felt a cool, unfamiliar draft. A thin brass circle flashed under the tile, as if someone had put a hoop there. The door to the storage room was ajar, and a steady buzzing sound came from below. Maks jumped out from around the corner, holding a torch from the study circle. "Can you hear it too?" he whispered, and Lena nodded, feeling a tremor in the railing. They descended into a concrete corridor where the bricks still remembered another school plan. A heavy grille with a sign waited at the end: "No admittance. Technical studios." Maks pushed it with his shoulder and the grating gave way with a groan, surprisingly easily. It smelled of dust, oil and something pungent that resembled a storm without the rain. Beyond the grating was a windowless room, full of hanging drawings of the sky and numbers. In the middle of the floor rested a brass ring, engraved with constellations and lesson numbers. When the clock in the secretary's office struck seven times, the metal responded with a low murmur. The air above the ring rippled like a hot road in July. "It's a resonance, or some kind of experiment," muttered Lena, but her palms were sweaty. Chalk arrows ran along the walls, and a forlorn projector blinked by the blackboard. A shadow slid out of the rippling circle, which cast no shadow on the floor. In the centre shone a panorama of the city, where lanterns floated above the canals. A bridge hovered between the two lunas, with someone in a hood looking down from the bridge. "Guardian of the Ring? You're late," said a voice, as if coming from several directions at once. Lena looked at Maks, and he only nodded, indicating the trembling edge of the gate. "If it's a trap, we're going back immediately," he said, though his voice trembled slightly. Just then, a new bell rang from the school corridor, and the circle flared more violently. A chill wave swept through the hall, and something moved on that side. "Leno, don't do anything stupid," whispered reason, but the leg took a step without asking.