In the small town of Borów, Janek's family moved only a month ago. Although Janek was only fourteen years old, the place quickly began to fascinate him, especially the old brick school, which for years had been haunted by empty windows and stories of strange phenomena. Until now, however, none of these stories seemed real to him. Everything changed one rainy night, when Janek accidentally noticed through the window of his room a flashing light in one of the broken windows of the school. The next day at school, Janek told his two new friends Zosia and Marta about it. They immediately began to speculate about who might be hanging around there. Was it really the ghost of the old caretaker that the elders had talked about, or perhaps thieves trying to hide the loot? Their imagination gave them different versions of events, but they decided to check it out for themselves. In the afternoon, armed with torches, notebooks and an old map of the town, the three friends dashed across the field to the overgrown entrance of the old school. For a moment they hesitated to enter, but curiosity won out. The corridors of the building were full of dust and the floor creaked as if to warn them of every step. At one point, Marta noticed a strange sign on the wall - shining in the torchlight, hidden under a layer of paint. Zosia, on the other hand, found an unusual key on the floor, as if made of black metal. Just as they were about to leave, something slammed the door behind them with a deafening bang. The torch lights began to dim, and in one of the dark corridors the familiar light that Janek had seen the night before flicked on. A quiet whisper sounded from the corridor, and a silhouette they did not recognise emerged from the shadows. The friends froze as they heard more footsteps clearly approaching towards them....