It all started on the first day of the summer holidays, when Zosia and Kacper decided to go to the Old Forest. On that day, the air was unusually warm and the sun flooded the world with golden light. The forest, which usually creaked and rustled, seemed unusually quiet today, as if it was waiting by itself for their arrival. Zosia was the bravest of the class and no one had as many ideas for fun as she did. Kacper, on the other hand, was able to find the rarest bugs in the grass and recognise every trace of an animal. On this day, they wanted to find something unusual - a treasure, a mystery, an adventure. As they trudged through the thick ferns and mosses, suddenly Zosia noticed something shiny under one of the roots. It was a small, silver key. The boy wanted to leave it behind, but Zosia convinced him to take the key just in case. They moved on, laughing and making up strange stories about dragons and witches. After several minutes of walking, the path began to narrow. Old, tangled trees grew on either side, their branches obscuring the sky. Suddenly, between the branches, they saw something completely unexpected - a tall stone tower, laced with vines and moss. The tower stood alone in a small clearing, as if it was just waiting for them. They ran closer. The door to the tower was locked with a padlock, the shape of which resembled a strange, writhing snake. Zosia immediately tried to use the key she had found. It turned out to be perfect - the padlock opened with a quiet click. The interior of the tower was full of secrets. Old portraits of people with strange eyes hung on the walls, and shadows crept across the floor. At the very centre stood a glass sphere that glowed slightly with a blue light. Next to it lay an old book with runes they did not know. Kacper held out his hand to the book, and suddenly the sphere flashed with a sharp light. The walls of the tower began to shake, and a soft, rustling voice came from inside the sphere: - Who wakes the Tower Keeper? Zosia and Kacper looked at each other with wide-open eyes, ready for what could happen in a moment....