Basia, Olek and Igor always looked forward to their holidays at Grandma Hela's house. Her house stood on the edge of the village, right next to a vast, somewhat neglected orchard. No one had picked fruit there for years; apples fell by themselves on the grass, pears lay among the tall nettles and cherries attracted the birds. Many times the children played among the trees, hiding behind the trunks and climbing the branches. This summer, however, they noticed something strange. One morning, Igor found a piece of shiny old coin under the oldest apple tree. It was heavy and had a strange mark engraved on it resembling the letter 'Z' intertwined with three leaves. He called his friends over and together they started looking for more traces. Basia claimed that it was definitely some old money that had been lost by someone a very long time ago, and Olek immediately started spinning stories about ancient knights and hidden treasure. When Grandma Hela brought them lemonade, they asked her for a story about the orchard. Grandma was silent for a while and then said: "They say that sometimes things happen among these trees that cannot be explained. But it's always better to check everything yourself." After these words she smiled, as if she knew something more. In the afternoon, the children returned under the old apple tree. They noticed that the grass in one place was trampled in a strange spiral shape. Olek concluded that this was surely the footprint of some creature. Igor suggested that they draw a plan of the orchard and mark all unusual discoveries. Basia, on the other hand, was betting that there might be something interesting underground. As the sun began to set, they made a decision: the next day they would come here again, equipped with torches, a compass and a magnifying glass. That evening they could not sleep, coming up with more theories. What is hidden under the old apple tree? Would they find anything else? When they stood at the agreed spot the next morning, instead of a spiral they discovered .... fresh footprints, leading straight between the blackberry bushes, where no one had ever ventured. Basia lowered her voice: - Someone had been here at night. Olek took out his torch, even though it was bright: - We have to see where these footprints lead. Igor nodded his head. With a beating heart, they moved towards the thicket, and the branches slid apart in front of them with a creak. Behind the last bushes they saw something they least expected....