At seven o'clock on Monday morning, the e-journal spat out something no one understood. A mysterious hour appeared in the Class 1C timetable: 'Field practice - Z-13'. Lena, the budding editor of the school's podcast, immediately switched on investigative mode in her head. Maks, her neighbour from the bench, only sighed and laced up his backpack. Room Z-13 did not exist in any school plan, yet the bell was calling. Under the arrow on the second floor there was only a plain wall, painted with fresh paint. - 'This is some kind of game by the management,' Maks muttered, taking a picture and sending it to the chat room. The physics teacher, Mrs Budnicka, passed them quickly, as if she pretended not to see them. Someone added with a marker under the announcements: "Where is Z-13?", and nobody dared to wipe it off. After lessons, Lena looked in the library archives, searching for old plans of the building. She found a map with the handwritten note "Zeta" and an arrow leading by the service lifts. - 'Don't hang around the basement today,' warned the caretaker, Mr Staszek, glancing at the clock. There was to be a trial evacuation at 5pm, so the corridors were quickly emptying. In the local government chat room, someone posted a rumour that Z-13 was a secret recording studio. Others joked that it was a cipher club that no one could find. When the sirens fell silent, Lena opened her locker and found a plastic token with Z-13 written on it. On the back were numbers that together formed the date of her birthday. With the map from the library, they reached the attic, under the old tower, where a steel door waited. There was a keypad at the handle; the token code went in without error and a brief buzzing sound fell. A chill and something like ozone after a thunderstorm blew from inside until they trembled. Inside, devices buzzed, monitors blinked and words appeared on one: "Leno, you're late". Maks pulled the headphones off his neck, as if they suddenly magnetised his skin. Lena's microphone on her phone flashed the recording icon on its own, though she didn't touch it. On the cursor screen, someone drew an arrow towards the other door. Someone stepped on the boards behind him and a quiet voice whispered: - Close behind you.