One rainy Tuesday, Lena, Filip and Zosia had an unusual idea: they decided to explore the oldest part of Lena's grandmother's house, about which strange stories always circulated. Their hearts beat faster as they descended the creaking staircase into the dark cellar. Only a single beam of light came through the small window, which illuminated a dusty trunk standing against the wall. - Did anyone ever open it? - Zosia asked, touching the lid. Filip looked at her with concern and Lena shrugged her shoulders: - 'Grandma said it came here with great-grandpa from a long journey. But she always asked us not to look in it. Curiosity, however, won out. The trunk opened with a quiet creak, and inside, instead of old clothes or books, lay a strange key and a piece of paper with a door drawn on it and the words: "Open then when you hear a whisper". Suddenly a quiet noise reached their ears, as if someone was saying something behind the wall. Lena found a door in the semi-darkness that she had never seen before. Without thinking, she slid the key into the lock. The door opened with a slam. All three felt a cool wind draw them in and suddenly they were in a world where the trees had leaves made of glass, the river flowed uphill and in the distance they could see the footprints of powerful paws on the silver sand. - Where are we? - whispered Philip. There was no time to answer, for a shadow slid out from behind a winding tree. Something, or someone, was watching them from hiding. The friends froze as a quiet, melodious purring they could not recognise approached....