At first glance, Primary School No. 12 looked completely ordinary: grey walls, a cool tiled floor and the sound of footsteps echoing in the corridors. However, Simon had already felt that something had changed here since the beginning of eighth grade. Perhaps it was a matter of a new tutor, Mr Rutkowski, or maybe he was just growing up and suddenly everything seemed less obvious. One cloudy Tuesday, with the rain drumming against the windows, Simon arrived at school earlier than usual. He leaned against the cold wall by the library, waiting for Maja and Igor, his best friends. He was browsing an English learning app on his phone when suddenly the door to the old wing of the school swung open with a quiet creak. Simon had never been there. The headmaster had once told him that it was a part of the building still closed since the renovation, and that students were not allowed in there. However, something about the sound caught his attention. He put the phone down, looked around and, taking careful steps, walked closer to the door. He peeked through a crack and saw a long, dimly lit corridor that ended in a padlocked door marked 305. At that moment Maja, with her always undeniably untidy fringe and notepad in hand, ran up to him. - What are you doing? - She whispered, seeing that Simon was looking into an unauthorised part of the school. - 'I think someone went in there, the door was open,' he replied, pointing to the ajar gate. After a while, Igor also appeared, and with an expression of curiosity on his face, he heard a brief summary of the situation. - Let's go there - suggested Igor, always ready to take risks. With their souls on their shoulders, they entered the dark corridor. The corridor seemed longer than it actually was. Their footsteps echoed twice, and the smell of the long disused room was almost suffocating. Along the way they passed dusty desks, old blackboards and posters from past years of school competitions. When they reached door 305, they noticed that the padlock was open, as if someone had looked in there a moment ago. Simon pushed the door open. There was semi-darkness inside. When they got used to the darkness, they noticed in the corner a large box covered with cobwebs and a blackboard on which someone had drawn a strange, complicated pattern with chalk. On the windowsill lay a spread-out notebook dated ten years ago. Igor reached for the notebook, but then a loud crack sounded. The door closed with a bang, and a quiet murmur came from the end of the classroom, as if someone was still there....