The Marie Skłodowska-Curie School was never a cosy place after dark. As the last bell rang out in the corridors, the walls seemed quieter, the shadows in the corners lengthened and the echo of footsteps echoed off the marble floors. Lena hated staying after lessons, but that day she had no choice - she and Kuba had to finish the history presentation they were to give the next day. In computer room 207, the keyboards were already silent. In the corridor, the sound of the door closing echoed every now and then, but the voice of Ms Iwona from the secretary's office reassured them: "You'll have another hour, kids. Then I'm locking up." Kuba, with a mug of coffee in his hand, sat comfortably in a creaky old chair. Lena was finishing moving the last pictures for the presentation when a brief but distinct sound came from the room next door. As if someone had jerked the bell standing on the desk. Although it was almost eight o'clock in the evening, there should have been no one in the school but them and Mrs Iwona. - Did you hear that? - Lena looked away from the monitor, frowning her eyebrows. - Maybe the caretaker? - Kuba looked at his phone, which had suddenly discharged to zero. The door to Room 208 was half-closed. They never went in there because it was an experimental room, full of dusty atlases, microscopes and models of old machines. There was always the smell of old paper and what Lena would call the dust of time. - Maybe someone forgot their keys? - whispered Lena, increasingly nervous. Cuba only nodded and pushed open the door. Inside was semi-darkness, the light from outside the window creating fancy patterns on the floor. There was indeed a metal bell on the desk. But something was wrong. The air in the room seemed thicker, and all the clocks on the walls showed a different time. Suddenly, a quiet rustling sound came from a dark part of the room - as if someone was moving a heavy notebook across the table. Lena involuntarily grabbed Kuba's hand. Then a soft, bluish light flashed just outside the window, blinking again and again, exactly to the rhythm of their quickened breaths. Before they had time to react, the door behind them slammed shut with a bang, and the bell on the desk rang once more of its own accord, louder than ever before....