In the old university building, where the corridors still remember the communist era, four students - Lena, Michał, Szymon and Patrycja - clearly stood out from the crowd. Not only because they always sat together in the last pew during history lectures, but also because they shared a fascination for puzzles and things that could not be explained. That day, the library was closing late and Lena put down her book on mysterious rituals from centuries ago with displeasure. Simon, searching through old catalogues, stopped and raised his eyebrows: - See this. - He showed them a yellowed sheet of paper with a sketched plan of the school. - Here is some room I have never seen. Patricia glanced over her shoulder: - 'The plan shows room 27B, but the door only has the number 27 on it, nothing else. Maybe it's an error on the part of the draughtsman? Michal smiled slightly: - Or maybe someone doesn't want us to look there. The decision was made quickly. They quietly slipped out of the library and headed through the empty corridor, which looked very different in this part of the building - dark, creaky floorboards, walls full of old photos and diplomas, and shabby doors with faded numbers. The door to Room 27 was closed, but a faint reddish light poked through underneath. - Does anyone smell that strange odour? - whispered Lena, glancing towards the door handle. Simon, as usual the bravest, gently pressed the handle. The door squeaked but did not give way. Patrycja rummaged through her backpack: - I have a lock pick. Dad taught me a few tricks for lost keys. A moment later the door gave way. Inside was semi-darkness, with only isolated rays filtering through the dusty window. In the middle of the room stood something no one expected - a large trunk covered with mysterious symbols. Next to it lay a rusty key and a piece of paper with the words: "Do not open if you are not ready to know the truth". Everyone looked at each other, trying to judge whether this was just a silly joke or something more serious. Michael reached out and touched the key....