The Stefan Banach School in Olsztyn was best known for being housed in an old, neo-Gothic red brick building. In the evenings, when the pupils had long gone home and the corridors were plunged into twilight, it resembled a castle from the outside. But on this day neither Lena nor Kuba were thinking about the architecture. Rather, they were worried about whether they would have time to rewrite their maths assignment before the first lesson. They squatted on the steps just outside room 204, counting on the support of Kacper, who usually had everything done. - 'Just don't tell me you forgot today too,' groaned Lena, seeing the look on Kuba's face. - Calm down. Everything... almost finished - muttered Kuba, pulling out a crumpled notebook. Everyone entered room 204 reluctantly. Mrs Sarnowska taught there - a demanding and relentless mathematician, but she was not the one who caused the most concern. There was always something wrong in that classroom: one time the light was flickering, another time someone complained about strange noises, and the bookshelf moved of its own accord. This morning, however, something was different. As the whole class gathered in front of the door, Lena noticed that a new poster had appeared on the wall next to it. It was titled: "Daredevils Wanted. Enter a world you don't know". The poster was neatly printed and signed simply: "Student Council". But that wasn't possible; Lena was on the council herself and no one was talking about any action. As soon as the door to the hall opened, the whole group rolled inside. Lena and Kuba sat in the last bench. During the lesson, the light started to vibrate again and Lena felt an increasingly strange uneasiness. Out of the corner of her eye, she saw that someone had written something on the blackboard in chalk that she had not seen before: "The chosen ones can see more". Instinctively, she looked at Cuba. He furrowed his eyebrows as he noticed the writing, which the teacher clearly had no idea about. Then, under the bench, something clicked quietly. Lena reached her hand under the tabletop and felt a small button. Without thinking long, she pressed it. At the same moment, the clock on the wall started ticking faster and faster, and the floor trembled slightly, as if something was moving underneath it. The walls of the classroom became shrouded in a strange milky haze. The teacher was speaking, but her voice sounded as if through a thick glass wall; the words stretched and swirled in the air. Lena felt something pull her and Kuba towards the steamed-up window, which began to slowly open on its own. Outside, the schoolyard was no longer there. Instead, one could see a dark blue sky, a pulsating faint light and a staircase leading nowhere. Lena and Kuba exchanged quick glances, both equally terrified and fascinated. Should they cross the threshold of room 204 and enter this unknown world? But before they had time to decide, a cry rang out from the depths of the classroom. Kacper, sitting a few benches in front of them, suddenly disappeared from their sight. In his place, all that was left was a scattered sheet of maths assignments and a a mysteriously glowing key. Lena and Kuba realised that they had just become protagonists in something that was just about to begin.