One spring morning Lenka woke up with an unusual premonition that something special was waiting for her. Outside the window, birds were singing and the sun was peeking into her room through the starburst curtains. Lenka looked at her red cat Balthazar, who was just stretching out on the soft cushion. - Today I would like to have a real adventure! - whispered the girl, stroking Balthazar's ears. After breakfast, Lenka decided to go to the forest behind the house. She walked quietly so as not to frighten the squirrels. Balthazar stayed close to her feet. Among the tall trees, the air was damp and smelled of moss. Lenka knew this forest like the back of her hand... and yet that day she noticed something she had never seen before. Under an old, huge oak tree, strange, glowing mushrooms appeared. Their hats shimmered with colours like soap bubbles! The girl crouched down and touched one of them. The mushroom moved and.... lifted into the air! - Miauuu! - cried Balthazar, pointing with his paw to something even more interesting. In the trunk of an oak tree was a small door, covered with green stones that sparkled in the sunlight. From behind the door came the soft sound of bells. Lenka looked at the cat, took a deep breath and grabbed the tiny handle. The door opened with a quiet creak, and behind it stretched a path strewn with glossy leaves, leading into the interior of the tree. - Come on, Balthazar! - she called out in a half-hearted voice. They both stepped inside. They immediately smelled the sweet fragrance of roasting chestnuts and heard quiet laughter. The path led deeper and deeper. Suddenly, a glowing butterfly appeared in front of them, flapping its wings at them. - If you want to enter, you must answer my question! - called out the butterfly in a thin voice and fluttered its wings so hard that they sparkled like stars.... Lenka and Balthazar looked at each other with excitement, as something they had never expected had just started....