I really like our old school in the heart of the town. It has a wide stone staircase and smells of chalk after lessons. In fifth B, everyone knows every creaky step and nook and cranny. My name is Lena and I have a memory for details. There's only one thing I don't understand about this school: the strange bell. Sometimes it plays a simple ding and sometimes a snippet of melody. Today, during Polish class at Mrs Żuraw's, I opened a reading book and froze. A sheet of paper lay between the pages, folded in four, written in print. It sounded like this: "Don't trust the bell. Come to room 21 when it plays the waltz". At a long break, I showed the card to Olek, who was sitting next to me. He raised his eyebrows and just whispered: "Let's check it after lessons". The rest of the day dragged on like chewing gum. When the last lesson came, the bell suddenly played a waltz. Mrs Crane furrowed her brow and we exchanged glances. After a while, the class deserted, so we headed for Room 21. The geography room was dark, with only the map shining in the sunlight. On the desk stood an old globe with the Arctic rubbed on it. On the back of a piece of paper a new sentence had been added, as if by magic. The command was visible: "Turn north three clicks". Olek held up the globe and I turned the pole three times. Something clicked and a narrow drawer with a brass key slid out. Beneath it lay a second scrap of paper with a cursive drawing of a clock. "The key does not fit the door. Look for the heart of time in the hall." I looked around and saw a large wooden clock above the blackboard. A tiny hole glistened on its side, almost invisible. I attached a chair and Olek stood up to assist me. I was raising my hand with the key when someone grabbed the door handle. A sound pierced the silence, and the shadows in the room twitched at once.