The old primary school never seemed fascinating to Karolina - creaky floors, dim lighting and the suffocating smell of dust. She walked past there every day on her way back from the library, but that evening something stopped her. It was after hours, and the corridor leading to the closed wing of the school opened to her with a quiet click, as if inviting her in. Karolina glanced at the exit door, then at her cat, Wafer, who followed her everywhere. When Wafer flashed through the ajar door and disappeared into the darkness, Karolina had no choice. She clamped her hand on the torch she always carried in her backpack and set off after him. The new part of the school looked different - the walls were covered with mosaics she had never seen before. As she moved her hand over one of the tiles, it moved slightly. Suddenly, she felt a chill under her fingers and an engulfing sensation, as if the wall might open at her command. Suddenly, footsteps echoed from the depths of the corridor. Karolina turned abruptly, her heart began to beat faster. It wasn't Wafer - those footsteps were too heavy. For a moment panic gripped her, but then she noticed something else. In the surface of the old, dust-covered mirror, instead of her reflection, she saw... movement. The image began to ripple like the surface of a lake during a storm. Karolina took a step closer. On the other side of the mirror appeared the silhouette of a boy her age, who looked at her with seriousness and held out his hand towards her, as if to warn her. Shadows began to emerge from behind him, moving unnaturally fast. On the other side of the corridor, the echoing footsteps were already very close. Karolina had to decide - stay in the familiar world or take a step forward and discover the secret of the portal....