As the last lesson came to an end, Olive, Bartek and Lena couldn't stop thinking about the mysterious note they found pinned to the door of their old school: "Whoever finds the missing note will discover the truth. But the truth does not always bring peace." These words ran through their minds all day until finally, just after dark, they met at the entrance of the old, abandoned building that had stood near the new school for years. Olive, the bravest of the three, opened the creaking door with a torch from her phone. "There's no one here," she whispered, though her voice trembled slightly. Lena looked at Bartek and raised an eyebrow. "What if they are? It's always been said that someone still lives here, like a caretaker who never wanted to leave the school." Bartek rolled his eyes. "Come on, they're just fairy tales for new students." They went inside. The air was heavy in the corridor and the sound of their footsteps echoed along the dusty walls. The darkness was almost total, and the shadows seemed to move to the rhythm of their breathing. At room 13, Lena stopped abruptly. "Look!" - she pointed to a dilapidated cupboard at the end of the corridor. A tattered notebook protruded from its ajar door, its cover bearing a faded name: Adam Majer. As they came closer, there was a quiet, metallic clang in the air, as if something had fallen to the floor in another part of the school. "Did you hear that?" - Bartek lowered his voice and Lena squeezed Olive's hand tighter. A faint light shimmered at the end of the corridor. Someone - or something - was really here. And it was looking straight at them. Olive took a deep breath and reached out for her notebook, but a shadow appeared from around the corner. For a brief moment it seemed as if all the doors in the corridor opened simultaneously with a protracted creak. The notebook fell out of the cupboard straight under their feet, and a cold breeze blew dust in their direction. Lena shrieked as the shadow approached - and then absolute silence enveloped everything. Who or what was waiting for them in the darkness of the old school?