The bell rang once, briefly, as if the building was winking at someone no one should meet here. It was 2:17 a.m., and Lena had on the Audacity screen slanted strands of audio from an interview recorded the day before. In her headphones, between the laughter of the choir and the scratching of the microphone against the interviewee's jumper, there was a clear school tone - the same tone they all knew from the morning jitters outside the physics room. Except that the school was asleep at that hour. High School Number 4 in the city was a 1960s modernist block, renovated on the outside and inside cobbled together all eras at once. Laminated blackboards next to faded display cabinets. Modern projectors in classrooms where the walls remembered chalk and the breath of matriculation. The most unusual was the C wing: unused for several years, closed to a glass door with frosted foil and a sticker saying "Technical area - unauthorised access prohibited". Behind them, a corridor cut off from the rest like a dormant body of a building. Since she was a child, Lena had been picking up sounds that others missed. That's why she hosted the school podcast "Between the Bells" and why she sat at her desk at two in the morning with a mug of cold coffee, rearranging vowels and pauses as if they were blocks. Baccalaureate was knocking on her door with advice from counsellors, plans, tables, and she was - instead of sleeping - staring at the thin beep of sound. A bell. A single one, to be precise. She rewound the recording backwards. The signal appeared and disappeared the same way each time it was played back. It was not a programme error. She opened a folder with footage from another day: choir rehearsal in the auditorium, same acoustics, same sound. Silence this time. She took her phone and texted Bartek, because Bartek was the only person still answering at that hour. 'Did you ever hear the bell ring at 2:17? - she sent. - I have it on the track from yesterday." The writing dots lit up almost immediately. "Check the metadata," Bartek wrote back. - Maybe your software clock has escaped. Or the server is testing the system at this hour. Write to the caretakers?" "Miss Baśka hates me since I threw the candy bar paper out of the window," - Lena wrote, smiling despite herself. The next day at school, the smell of wet jackets and floor polish mingled as always with the smell of chalk. Lena and Bartek met at the coffee machine. Bartek smelled of physics: a briefcase, cold air and slightly too ambitious deodorant. He was a walking hypothesis that needed testing. - Did you take it down to the real thing? - He asked when Lena turned on his headphones to a foul passage. He closed his eyes. The moment the sound ran across his face, he twitched slightly. - 'That's our ringtone,' he said with conviction. - But where did the time come from? - He glanced at her screen. - 2:17 a.m. Silly time for tests. - He pondered. - The new system is in the C wing. I saw the technicians bringing the amplifiers in there. They said it was the thickest walls and the best wiring harness. C wing. Lena felt a slight shudder, but not the kind from the movies. More like the shudder of logic suddenly turning naughty. - 'So the bell could only go on there,' she said. - When the rest of the school was disconnected. - Or the sound went down a side line. - Bartek rubbed the back of his neck. - Anyway, why test something in the middle of the night? - He lowered his voice. - Baśka says it 'pulls' there. - You know I don't like urban legends in school uniforms - Lena snickered, but the image of the frosted glass from the C-wing stuck to her eyelids. - I'll ask. For the hygiene of the facts. Ms Baśka sat at the gatehouse with a crossword puzzle and a mug of tea, like a fortress. She had hair so stiffly pinned up that you could leave a paperclip on it, and a gaze that had the gift of stopping students in mid-motion. Lena stood so that the sun from the courtyard did not glint in her eyes. - Miss Baśko, because... - she began with a smile that had as much sugar in it as she could afford. - That bell in the night... Does anyone do anything there in the C-wing at two o'clock? The usher looked at her as if she had heard something about an un-snowed step. - 'What's it to you, miss? - she grunted. - When you're at home at this hour, you don't listen to nonsense. And if you're at school at this hour, you should have a key. - She sipped her tea. - 'We've got new servers here, the headmaster fancied making everything 'smarter'. Sometimes something flashes. The worst are the fire tests. Once it switched on on a Saturday. I thought my heart would go out down the corridor. - So someone's going in there? - Lena didn't let up. - At night? - The maintenance man. And sometimes nobody. - Ms Baśka was leaning over the crossword puzzle, but her voice had softened. - Don't look in there. There are ladders, cables, water dripping down the wall. When it's windy out there, people do stupid things. There were diplomas hanging in Director Kwiecinski's office that looked as if they were to congratulate everyone who came in. Lena came in with a microphone because she had an interview scheduled about the new regulations for the use of the computer labs. The principal spoke in a smooth voice about 'openness to innovation' and 'digital leapfrogging', and Lena listened, ticking off questions. As the recording came to an end, she ventured one private one. - 'Mr Director, and that bell amplifier you installed is in the C-wing, right? The director's slanted eyebrows twitched slightly. - And from where you... - He smiled for form's sake. - Yes, that's where the room with the servers is. The best conditions. Please don't record this. - When Lena turned off the recorder, he added more quietly: - And please don't let anyone go in there. We didn't close off the wing for kids to play in. in the penguins of curiosity. There is a procedure. If something lights up, it means someone is working. 'Curiosity penguins' followed Lena for the rest of the day. There was a ringing in her ears at 2:17 a.m. Maybe it was a test. Maybe a mistake. Maybe someone's minor oversight. Except that when she returned to the assembly after class, the sound she already knew sparkled in her headphones like the breath of a forbidden corridor. Once, briefly. Exactly the same tone. That evening the choir had an extra rehearsal for the competition. It stretched out, as usual, because someone had lost their notes, someone had missed the bus, and someone else was afraid of high notes. When the last "la-la-la" quieted down, the smell of disinfectants and fatigue wafted from the auditorium. It was after twenty-one by the time Lena packed up her microphone and walked down the corridor past wing C. Ms Baśka was handing the key to the geography room to the duty officer; it was windy outside, rain blurring the lamps on the pitch. Her face was reflected in the frosted glass of the C wing - a little blurry, a little alien. "Don't look in there" - sounded Ms Baśka's voice. "There is a procedure," added the director in Lena's head. Yet she stood, seeing her own breathing as if it were a fog, and moved her gaze down the dark corridor beyond the glass. Behind the film there was only darkness and a row of hazy squares: doors to technical rooms, storage rooms, panels. At least, that's what the evacuation plan said. Bartek wrote: "Are you still in school?" "Mhm. I'm going home." - she wrote back, but her fingers slipped, her thumb hovering over another possibility. - "Maybe I'll look in...?" - she deleted it quickly and sent just an emoticon with a sleepy smiley face, as if that closed the subject. A slat creaked from the ceiling above the frosted glass. The wind rustled the old windows. In the same second that Lena turned around, the light behind the film came on in one long, milky strip. Not like in a normal corridor, where the lamps turn on one at a time, reacting to movement. Here the flare was even, firm, like the gesture of someone who doesn't like half-measures. Lena froze. She squeezed the straps of her bag in her hand. A feeling ran down her back that had no name: a mixture of curiosity and responsibility that starts jumping like a ball in a closed box. There was no sound coming from behind the glass. There are always noises in school buildings - drains sighing, pipes talking to each other in whispers, floors creaking like old memories. Now there was a silence so complete that she could hear her own pulse. - Hello? - she said palely and immediately laughed at herself inside. Who was she saying 'hello' to through the film? In that silence, the bell rang. A single tone, a minimalist 'ping' that usually chased students out of their desks. Here it sounded like a private sign. Lena did not move away. She did the opposite: she walked closer. She was in her own school. This was her corridor, her bell, her microphone, her responsibility. And her penguins of curiosity pushed forward. At palm level, on the C-wing side, was a small panel with a diode. When Lena stopped in front of it, the LED flashed. Once. A second time, more slowly. And a third - clearly, as if responding to her breath. Then nothing. She stood, staring at the spot until the letters of the 'Technical area' sticker began to tremble from her own staring. - Lena! - From the end of the corridor came the voice of Professor Wojnar, who was closing the auditorium. - 'We're going out.' - His footsteps approached slowly. - Don't stand there, you'll get blown away. - I'm coming," she exclaimed, without taking her eyes off him. - Just... - she paused, because at the same moment, under her finger on the other side of the glass, where the silver handle began, something vibrated slightly. The light flashed rapidly, again and again, in a short sequence, as if someone was entering a code. The lock, which had made no sound for years, responded with a quiet, dry click. Lena tightened her fingers on the strap of her bag, her heart whimpered with another thump and then the handle on that side moved once more, this time clearly, downwards.