The school, while resembling thousands of other buildings from the outside, was teeming with a completely unique energy inside. The creaky old staircase and age-old walls of High School No. 7 had witnessed many stories, but none equalled the one that began one Thursday morning. As the bell rang to announce the start of lessons, Alan pushed open the door to Room 103 with more resistance than usual. He was followed by Karolina, somewhat thoughtful, and Darek, holding a mug of coffee and a notebook strewn with drawings of dragons and spaceships. They always sat together, because only in such a line-up did no teacher's question seem so threatening. On this day, however, something was different. On the blackboard, right next to the map of Europe, someone had written in chalk an enigmatic sentence: "If you want to know the truth, look for the key at midnight." Karolina looked around at her friends. - Who could have written that? - she whispered. Lessons passed more slowly than usual. Alan kept glancing at the clock, while Darek tried to work out the message by scribbling strange symbols in his notebook. When the final bell finally rang and the school began to empty, all three of them still had the words in front of their eyes. They couldn't wait for midnight. At that hour the school was locked up, the corridors plunged into darkness. But when they met at the side entrance with torches and beating hearts, the door swung open of its own accord, as if someone was already expecting them. They entered without a word. The shadows on the walls rippled uneasily and the echo of their footsteps echoed ominously. Suddenly, Darek noticed a pale patch of light at the end of the corridor. - Can you see it? - he whispered. - I think it's coming out of our hall... The silence was almost palpable as they approached the door of room 103. A barely audible whisper came from inside. Karolina reached for the door handle and....