Anne loved going to the School Under the Coloured Oak. Every morning she was happy to run across the green square where the huge, spreading tree grew. Like her, her best friend Kuba also liked the school, especially when there were interesting lessons and games at breaks. One morning, in the middle of autumn, when the leaves on the oak tree were already all the colours of the rainbow, Anna found something strange. She was the first one in the courtyard. Between the red leaves she saw a small object, gleaming in the sunlight. It was a very old, brass key. It looked like it had been made a long time ago and had tiny leaves engraved on it. Kuba immediately joined her. - 'What have you got there, Anna? - He asked, looking at it curiously. - 'I think it's a key,' said Anna, handing him the find. - But I wonder, from what? A moment later the bell rang and the children ran to class. During the lesson, Anna could not stop thinking about this key. She wondered if it matched one of the lockers at school or an old box she had once seen in the library. At break time, she agreed with Kuba that they would try to check it out together after lessons. First they went up to the cloakroom, but there all the locks were modern. Then they headed to the library. The librarian, Ms Ewa, was always happy to tell stories and knew all sorts of interesting facts about the school. On this day, the library was almost empty. In the corner stood a very old box that the children had seen more than once, but had never been opened. It looked like it had been closed for a very long time, and a small oak tree was painted on its lid. - Shall we try it? - whispered Kuba, looking at Anya with a glint in his eye. The girl carefully slipped the key into the lock, and Kuba held her hand to stop her shaking. Suddenly something quietly startled and....