The clock in the corridor of Copernicus High School had long since stopped working, but that didn't bother the students - after all, no one was looking at its hands. On that day, Asia, Kuba and Lena didn't even manage to notice when eight o'clock struck, because they were busy with their own conversation, standing under locker 47. Lena, who had once again forgotten her notebook, was looking for an excuse, and Kuba was considering whether to try downloading today, when suddenly... the locker started to shake. - Is it just a draught? - chuckled Kuba, feigning indifference. Suddenly, there was a quiet scratching sound from inside the metal locker, which transitioned into clear, slightly squawking words: - Hey! Watch out with that shaking, I've got business here! Asia jumped all the way back. Lena dropped her backpack. Kuba looked at them uncertainly and then, trying to keep his cool, opened his locker. On the shelf lay a crumpled notebook, an old sandwich and... a key with an unknown symbol. - Who said that? - Lena asked in a whisper. - 'Me,' the key said quietly, bouncing on the shelf. - I'm guarding the passage. And I haven't had a visit in years. All three of them froze. They had heard stories about ghosts in this school, but never about... a talking key. From around the corner of the corridor came the quick footsteps of the history teacher. Asia took a quick glance at the symbol on the key - it resembled spinning numbers. The key beeped even louder: - If you don't want anything more than sandwiches to disappear, you must hurry. The break was over. The door of classroom 12, which they were about to enter, looked very different from usual today. There were strange carved marks in the wood that hadn't been there before. Lena turned to Asia and Kuba, her eyes wide open. They all understood that something had just started. Before they could take another step, they felt a cold blast on the back of their necks and heard the murmur of whispers coming from the cupboards, walls and floor. Everything around them began to speak - and had something important to tell them....