The S. Lem School had its secrets. The older pupils joked that corridors changed at night and underground tunnels led into the unknown. However, Karolina, Wiktor and Lena knew that jokes often had a grain of truth in them. On Friday afternoon, tired from struggling through maths and biology, they came across something strange. There was an unusual noise throughout the school, with teachers running around the corridors with some sort of notepad, and the principal locked in his office sending suspicious emails. "Have you noticed that the timetable shows room 212 and no one has ever seen it?" asked Lena as they waited in the corridor for an extra lesson. "Maybe because she's not there?" Victor shrugged his shoulders, trying to hide his interest. Karolina glanced at the plan hanging by the secretary's office. In fact, Room 212 appeared several times - always during the hours when the school was officially closed. Intrigued, they began to check the next floor. They bypassed the crowds and entered a wing where no one had looked in years. Suddenly, Karolina noticed a door. It didn't have a number, but under the light of the phone they saw a faded trace: 212. The door was closed, but there was a faint, bluish light seeping from underneath. Victor pushed the handle and the door gave way with a quiet creak. Inside was no ordinary classroom - there were old benches arranged in a circle, and luminous shadows ran along the walls. Suddenly they heard a crash and someone - or something - moved in the depths of the room. Lena held her breath and Karolina took a step forward. Suddenly, the light dimmed and strange writings began to appear on the blackboard, as if someone had written them with an invisible hand. Then, from behind one of the desks, there was a deafening whisper: "I knew you would come here eventually...".