It all started on a chilly March morning, when Tosia and Igor set off along a path through the forest, as they did every day to school. Only that day they had decided to take a shortcut, cutting through a slightly wilder part of the forest, where the trees talked to each other through the rustling of the leaves, and sometimes the wind carried a barely audible laugh from afar. Tosia was a year younger than Igor, but much more adventurous. Igor wanted to have everything planned. But that morning, when they both spotted a silvery squirrel running under their feet, neither could resist curiosity. The animal seemed to invite them to chase it, which seemed like a simple joke until they followed it deep into the forest - where they had never been before. The squirrel stopped by a massive, moss-covered oak tree. The children approached cautiously and only then did they spot a door on the trunk. Tiny, with a brass handle, carved as if especially for them. Tosia touched the handle and the door gave way with a protracted creak. From inside the tree came the smell of freshly baked bread rolls and cherries. Behind the door, steps led down, winding among the roots. Igor walked right behind his sister, holding on carefully to the handrail braided with twigs. At the bottom, something extraordinary appeared to their eyes: a vast underground hall, lit by the glow of hundreds of skylights, while colourful leaves floated in the air and formed themselves into inscriptions on a blackboard. Around the tables sat students. But they were no ordinary pupils - some had furry tails or multi-coloured wings, others had slightly too long ears or feelers, and one girl had a blooming tulip on her head. At the lectern stood a teacher with a hairstyle resembling a tangled ball of thread, and her eyes sparkled with violet. Before Tosia and Igor had time to step back, the teacher smiled broadly: - Hello, newcomers! I've been waiting for you. I invite you to sit down, the lesson starts in a moment, and today we have something really special to discover! At the same moment, a silvery squirrel climbed onto one of the desks and began to speak in a human voice, causing a quiet murmur of excitement among the students. Igor opened his mouth in surprise, and Tosia squeezed his hand. Everything pointed to the fact that on this day they would not learn addition and reading as usual, but would take part in something that would change their lives forever. When the girl with the tulip on her head slipped them two coloured feathers and whispered: "They will be needed for the first task", a crackling sound came from above - as if something was changing on the surface of the earth, and the magical light in the room flicked on more violently than before....