It was Wednesday morning, eight o'clock, and heavy dark blue clouds hung in the sky. The deserted corridors of High School 3 were slowly populated by students shuffling about with mugs of coffee in their hands, covering their yawns with thickly wrapped scarves. The fluctuation of energy - from the slight excitement through the greyness of the routine - could be felt like a fog hovering just above the floor. Susanna, who has always attached importance to punctuality, was already waiting in front of room 224, where the biology lesson led by the well-liked Professor Bartosik was about to start. Igor was standing right next to her, leaning with his back against the wall, fiercely swiping his finger on the phone screen. The two of them were joined by Lena and Filip - the four of them were united by trips to concerts and a love of puzzles. As it chimed eight-five, the classroom door opened with a quiet creak. "Come in!" - called out Mrs Bartosik, and the students began to take their seats. Just a moment later, the story of animal evolution was interrupted by the sound of chairs being moved - the late Paul burst into the classroom, dishevelled as usual. Mrs Bartosik sighed and reached for the attendance register. She did so, however, to no avail - her hand encountered only an empty tabletop. "Strange... I just put it here a moment ago," she muttered under her breath and began frantically searching through the piles of papers. Igor looked meaningfully at Zuza. Lena shook her head. The attendance list was always on the desk, stacked perfectly evenly by the edge. The disappearance of this piece of paper seemed impossible, and yet it was gone. Mrs Bartosik began to ask questions about whether anyone had seen the list or had accidentally taken it. She was answered by silence and a slight commotion among the pupils. In an instant, the classroom became thick with unspoken thoughts. Philip, who always had an eye for detail, noticed something that caught his eye - there was a small black notebook lying on the windowsill, completely incongruous with the interior of the classroom. He looked at the booklet, which looked quite old, with a worn-out cover. Then Igor leaned over to Zuza and whispered: "It might have something to do with what happened yesterday after class. Do you remember the noise on the second floor?" Susanna felt a slight shiver. For a moment no one spoke, until Lena spoke up in a slightly trembling voice: "Maybe someone hid the list on purpose to hide that he wasn't there yesterday? Or... maybe someone wants to tell us something?" Mrs Bartosik decided to go out to the secretariat to ask for a new list. That's when Filip couldn't stand it and bolted from his seat. "I need to see this up close," he whispered to the rest of the pack and dashed to the windowsill before anyone had time to stop him. As Philip touched the notebook, they all heard a quiet, strange sound - as if something underneath had moved across the windowsill. Susanna froze. Lena squeezed Igor's hand. Suddenly the emergency bell sounded in the classroom and the door slammed shut with a clatter. Everyone looked at each other in horror, and Philip looked at the package with wide-open eyes. In his hand was a piece of paper torn from a notebook, on which someone had written one word in clear, slanted handwriting - their own names. A strange silence fell in the classroom, broken only by the quiet buzzing of fluorescent lights. No one knew what would happen when they opened the notebook to the next page....