The old school on Kwiatowa Street had its own legend - telling of undiscovered cellars and strange phenomena that supposedly took place long ago. For most pupils, it was just a fun topic of conversation during breaks. But for Lilka, Antek and Zoska, these rumours were something more: an invitation to adventure. It was Friday, just after the last bell before the summer holidays. The corridors were emptying, the lights in the classrooms were going out and the caretaker was closing the lockers. Lilka, the lowest of the three, always wanted to see more than the adults allowed. Antek, her older brother, had a talent for opening locks and an innate courage. Zośka - their friend - loved puzzles and hoped to discover something out of this world. - Ready? - whispered Lilka as they slipped out of the cloakroom. They descended the creaking stairs to the basement, where the light of the torches cast irregular shadows on the cracked plaster. The old door, which was usually locked, gave way this time under Antek's pressure. Inside, it smelled of dust and rotten paper. After a minute of rummaging among the bookcases, the boy noticed something unusual on the wall - a large mirror in a brass frame, almost invisible behind a pile of old maps and atlases. - Who would hang a mirror here? - muttered Zośka, running her finger over the sheet on which their distorted silhouettes were reflected. Suddenly Antek noticed that his reflection was blinking at him, while he did not move an eyelid. Lilka froze, and Zośka pinched her arm. Before they had time to think about it, the mirror began to ripple like water. For a moment they thought it was their imagination playing tricks on them, but then a quiet, trembling light emerged from the sheet. - What now? - Zośka asked, squeezing Lilka's hand. Antek already knew - this was no ordinary portal. His hand, stretched towards the light, disappeared on the other side of the mirror like a stone thrown into a lake. For a split second, he felt a chill, as if he had touched air from a distant, unknown land. It pulled him all the way in - and before Lilka or Zoska could react, they too felt something pulling at their hands. A moment later they found themselves in a place that resembled nothing they had ever known. The sky was a dark blue colour, and among the silvery trees swirled creatures they had never seen before. From over the hill came the clatter of hundreds of little feet. Lilka grabbed Antek's hand, and Zośka tried to see what lurked among the shadows. - Where are we? - whispered Lilka. Then a figure appeared at the edge of the path. It had wings made of something that looked like sparkling light, and a gaze so penetrating that Lilka felt a shiver run down her spine. The creature picked up an oblong key-cut from a shining crystal-and slowly began to move towards them.