Everyone in the Old Town knew that the abandoned grammar school on Węgierska Street was no ordinary place. For years, the elders had said that if you dared to cross the threshold after dark, you might not come back the same. Lena, Kacper and Igor had been planning this trip for a long time. They were curious if the old stories about the hidden shelter, invisible passages and strange sounds were just fairy tales or something more. In the evening, when the town was already falling asleep, they met under the high, rusty fence. Lena glanced at her watch - 11:07 p.m. Igor, as usual, pretended not to be scared at all. Kacper had a torch and an old camera with him because, as he said, "maybe we could take a picture of the headmaster's ghost". They walked through the hole in the grid and stood by the dilapidated stairs leading to the main entrance. The door appeared to be ajar. The pale glow of a torch illuminated bits of detached wallpaper, scattered benches, old photographs on the walls. - Do you hear that? - Lena stopped. Amidst the wail of the wind, there was a quiet rustling sound. Kacper pulled out his camera, Igor laughed nervously. A whisper came from the corridor to their left - as if someone just down the hall was saying their names indistinctly. They stood still for a moment until Lena dared to go further. The corridor stretched into darkness. At the end was the double door to the former biology room. Igor, wanting to prove his courage, grabbed the handle first. The door opened with a protracted creak. A strange chill emanated from inside the room. As they stepped inside, Kacper's torchlight brought out a shape from the darkness. Something - or someone - stood by the blackboard, motionless, all in shadow. Suddenly they heard approaching footsteps in the corridor. Lena squeezed Igor's hand. Should they hide or run away? The footsteps were getting louder. Kacper picked up his camera, trying to take a picture of the mysterious figure at the blackboard. Then the torch went out and the room was plunged into darkness. For a second no one stirred - until, in the silence, they heard a sudden, shrill creak just behind their backs....