Franek lived in a small house at the edge of a colourful forest. Every day, he and his cheerful dog Pikus went for long walks among the trees. One sunny morning, when the dew was glistening on the grass, Franek noticed Pippy sniffing out something interesting under a big old oak tree. - What have you got there, Pikuś? - asked Franek, running closer. Pee-wee barked happily and his nose almost touched the ground. Under the oak tree lay a strange wooden key, all covered in leaves and a piece of cobweb. Franek picked up the key and looked at it in wonder. It was heavy and old, and had a small drawing of a bird carved on the handle. - This must be a magic key! - exclaimed the boy. Suddenly he noticed that not far from the oak tree, among the roots, there was a door he had never seen before! They were tiny, barely visible in the moss, and had exactly the same drawing of a bird as the one on the key. Franek's heart beat faster. He and Pikus looked at each other and slowly walked closer. Would they dare to open the mysterious door? What could be hiding inside?....