Every Friday Lena went back to the gravel pit behind the town. She was eleven years old and her pockets were full of flat pebbles. She looked for the ones that clanked under her fingernail like porcelain. That evening the sky was pale and the water smooth as glass. The wind crackled in the reeds and a hollow echo came from the pier. Lena crouched by the shore and reached for a stone unlike any other. It was warm, though the day was cool. A thin line ran across its surface, like the drawing of a door. - Olek! - she called out and waved her hand. The boy ran up with his bike and jumped down onto the sand. Lena put the stone on her hand and he put his ear to it. The stone buzzed really quietly, like a cup hit with a spoon. - Can you hear it? - she asked. Olek tapped the stone with his finger. The surface of the lake trembled, although there was no wave. Then a single sound came from the depths, like a bell hidden beneath the water. Lines of light flashed under the mirror, arranged like streets on a plan. Lena drew in a breath of air. - 'It's a city,' she whispered. The bell rang out a second, a third, as many as thirteen times. With each note, the stone trembled harder and the water slid apart into steps. They glowed pale, like the moon on a plate. The reeds leaned, as if someone was passing by. - 'Maybe we'd better go back,' said Olek, but he didn't move from his seat. Lena came closer and stretched her hand over the first step. A cool whirlpool rose from below and touched her fingers. Then something shimmered under the last step. The shape was human, but it floated like a shadow. Lena withdrew her hand, and the stone in her palm suddenly buckled thinly. Just off the shore, the water tightened like a foil and then broke into a single semi-circular hole. Someone from the depths looked straight up.