The library in their town was a peculiar place. It wasn't just dusty bookcases full of books, or soft armchairs in which to hide for hours on end. For Julia and Kuba, it was a temple of secrets, as each bookcase seemed to hide its own secrets. And yet one day they stumbled upon something that even they had not expected. On Wednesday after lessons, Julia crossed the threshold of the library with her schoolbag hanging over one shoulder. Kuba was already waiting for her, rummaging through a pile of books on dinosaurs. - Come on, I'll show you something! - he called out in a whisper, pulling Julia towards the oldest part of the building. There, behind the bookshelves, was a forgotten corridor that led to a room that had been locked until now. For years the door had been bolted, but today were slightly ajar. Inside, it smelled of old paper and dust. In the middle stood a huge mirror in a gilded frame that looked like it remembered the days of their grandmother's grandmother. Julia glanced at her reflection and for a moment she had the impression that she saw there not herself, but a hazy silhouette in a strange hat. - Can you see it? - asked Kuba, coming closer. - What? - she tried to take a step back, although something was drawing her closer. - 'That mirror... I think it's moving - Cuba said, and his fingers almost touched the surface. And then something strange started to happen. The surface of the mirror rippled like water, and the light in the room dimmed, as if the whole place was going to disappear. Julia felt as if a wind was blowing around them, even though the windows were tightly closed. There were sheaves of light and shadows of strange figures in the mirror. From behind the glass, a completely different world looked out - full of tall trees, strange creatures and a castle floating in the air. Someone on the other side was reaching out to them.... Julia and Kuba exchanged glances, their hearts beating faster than ever. What would happen if they went through the portal? Should they grasp this mysterious hand? Little did they know yet that this decision would change their lives forever....