Gaia, Leon and Little Christopher loved spending time in the cottage on the old oak tree. The cottage was built high up, between thick branches, and the window looked straight out onto the quiet, mysterious forest. One evening the children decided to stay there for the night. They had torches, a blanket and lots of snacks. They were all excited! It was their first night in the tree house. As dusk fell, the forest became completely different from the daytime. From behind the leaves, rustling could be heard. Gaia shone her torch, trying to see what was moving there, but only dancing shadows appeared in the light. "Maybe it's a hedgehog?" - whispered Leon. "Or an owl!" - added Christopher. Suddenly, a soft thumping sound reached the cottage. The children froze. Something was scraping at the floorboards from underneath! Leon bravely moved closer to the entrance. "We should see what it is," he said quietly. Gaia grabbed his hand and Christopher took his plush sword in his hand. After a moment, the thumping fell silent, and instead, a soft, melodious whistling sound came from the darkness. The children looked at each other with wide-open eyes. What could make such a sound in the middle of the night? Then suddenly a tiny light twinkled outside the window. It came closer and closer and....