Monday's rain streaked across the windows like inscriptions someone had typed in slow motion. Primary School No. 23 had two faces: the new wing of glass and metal, where it smelled of fresh paint, and the old one, overgrown with ivy, with narrow corridors and slippery stairs. Lena liked that old wing. When silence fell, you could hear the walls breathing. She walked inside, shrugging off her hoodie, with her skateboard strapped to her backpack and her headphones rolled up in her sweatshirt pocket. She was of those people who listen first and then look: someone's footsteps, the creak of a door, a single tone from the music studio in 'two'. She was friends with the bells like nobody's business - she knew how many seconds each lasted as it sounded from the megaphones near the ceiling, and she liked it when there were strange pauses between the tones, like electronic breathing. - Did you hear that? - Basia jumped out from behind a pillar with a camera slung over her shoulder. - They changed the plan. PE at eight, really? - Seriously,' Marcel muttered, reaching in with his pockets stuffed with cables and a box of chewing gum. - But watch this - he lifted his phone. - 'There was a drone recording the stadium at night. Don't ask where the drone came from. The pitch was empty, and at three o'clock in the morning the light in the window of the old common room came on. - 'Maybe Mr Gienek left it on,' snarled Basia. - Or the ghost of the duty officer. Lena did not reply. She stopped when the bell for the first lesson rang. The sound rolled down the corridor, bounced off the white door with the numbers 214, 216, 218, and abruptly stopped in a strange place, as if someone had jammed an audio file. After a brief pause, it came back, but it had something not-yet in it: shorter, longer, longer, shorter. Lena furrowed her brow. She remembered camping by the lake and Marcel's torch flashing dots and dashes into the dark forest. - Can you hear it? - She asked quietly. - As if... - I know, I know,' whispered Marcel, as if they were talking at a test. - I have it too. Like a signal. Room 214 smelled of chalk and whiteboard marker. A mock-up of a medieval tower made of paper stood on a bench, and someone had stuck a cutout of a poster about a family picnic on the window. A new history teacher entered the classroom wearing a long graphite skirt and with a thick notebook under her arm. - 'I'm Mrs Rymsza,' she announced. - We will start the year with a project about our school. In the library, in the old wing, lie the chronicles and plans of the building from years ago. The team that comes forward will keep a class archive. - She smiled slightly. - Be warned, part of the basement is off limits. Refurbishment. Please do not go down there without a guardian. Lena raised her hand first. - I can be in the team. - Me too - said Basia and Marcel at the same time. - 'Excellent - nodded Mrs Rymsza, handing them a laminated piece of paper stamped 'Permission to access the archive reading room, until 1 p.m.'. - The library opens into a long corridor. And now, the textbooks. Lena listened with half an ear for half the lesson. The other half was still dissecting the bell. Dot, dash, dash, dot. Under her fingers she drew a rhythm in her notebook as if it were a score. "P-i-w..." - was suddenly forming in her head. She tightened her pen. At break time they squeezed between the tables under the windows, where the 7b girls were exchanging tiktoks, and ran to the library. In the new wing everything was bright and almost odourless. In the old one there was again a mixture of paper, dust and floor polish. - Good morning, Mrs Nelu - they bowed to the librarian with grey hair clipped together. - Excellent children - said Mrs Nela with a smile. - We have the chronicles in the reading room on the left. Just please be careful, these are the only copies. The reading room was small, with a table that remembered the days when mums were still at school. On the shelf lay thick volumes: "Chronicle 1986-1995", "Chronicle 1996-2005", "Evacuation plans - archive". Basia immediately reached for the chronicle from the 1990s, Marcel for these plans. - Look - Lena moved her finger over an old diagram of the building. - "Staircase A0: transition to the technical level, the so-called zero level". - Level zero? - repeated Basia. - 'We don't have any "level zero" on the plans at the entrance now. - 'Well, that's right,' Marcel took out of his rucksack a new evacuation plan that had once fallen off the notice board and strangely ended up in his collection. - See. Here the A staircase ends at the basement. There is no "A0". Lena swallowed her saliva. Next to her in the chronicle, Basia found photos of theatre performances and entries about competitions. One of the chapters was strangely thin, as if something had been taken out of it and pasted again. A fresher page and an uneven edge were visible. - 'It's kind of glued together,' muttered Basia. - 'You mustn't tear, don't look at me like that. But see next to it: the picture 'Preparatory class - group 0'. I've never heard of that. - That was a long time ago - said Mrs Nela from behind the bookcase, as if she had a seventh sense. - Different programmes, different names. They were remodelling something back then, but that's not my thing. Lena cast her gaze over the old plan once more. Staircase A. Arrow. The level below the basement, drawn in a line paler than the rest, as if someone didn't want it to be too visible. After the bell rang for the next lesson, there was a strange rhythm again. Lena could no longer pretend it was nothing. She took a page out of her notebook and started writing dots and dashes, listening carefully, counting her breaths between the signals. She crossed out, corrected, until finally she wrote in capital letters: P I W N I C A. - 'This can't be a coincidence,' Marcel said quietly as she showed him the piece of paper. - Either someone is making fun of us, or... - He broke off. - We're going on a long break. - Don't be ridiculous - Basia nervously wrapped a rubber band around her hair. - 'It says in the regulations 'don't go down'.' Mrs Rymsza said. And Mr Gienek is going to get mad. - 'We don't have to go down,' Lena said, although her heart sped up. - 'We're just going to check what "A0" is. We'll have a look. If anything, we'll turn back. Agreed? Basia sighed. - 'All right. But if we get caught, you say it's your idea. The corridor in the old wing downstairs was cooler. Old photographs in wooden frames hung on the walls: students from the eighties with bows in their hair and boys in patterned jumpers. A board creaked underfoot, the creak of which every teacher on duty knew. On the door on the left was the sign 'Decoration storage', on the right 'Sports equipment storage'. Further down was a staircase. Above them, a milky glass lamp flashed like an eyelid. - 'This is it here,' Lena said in a whisper anyway, even though no one was around. - Staircase A. They went even lower. When they touched the handrail, they felt a chill. At the bottom hung a placard with scratchy letters "Basement - access for staff only". Behind the plaque was a narrow corridor and a steel door with a small card reader. They didn't look like part of an old school. More like the entrance to the server room. - Really? - Basia crouched down and looked at the lock. - Since when did we have readers? - We've always wanted one," muttered Marcel, who was already putting his school ID into the reader, because why not. The reader didn't even beep. On the left, by the skirting board, the dust had settled into a thin layer. Lena crouched down next to Basia. She saw the imprinted soles - indistinct, as if someone had passed this way a day or two before and pushed something heavy through, which blurred the marks. Next to her lay a thin carpenter's crayon, too new for a forgotten corner and too incongruous for the basement of a school. - 'Someone's been here,' she whispered. - 'Or is,' Marcel added, peering through the narrow gap between the door and the doorframe. - 'Look, there's some light on that side. Or it's reflecting from a lamp. Or... A third bell rang from upstairs. It was muffled in the basement, as if someone had covered the speaker with a blanket. Lena felt the sound break down in space into short and long tones, as before. The skin on the back of her neck tightened. At the same instant, without any touch, the reader by the door flicked. Once, a second time. Quietly, almost inaudibly, something clicked inside the lock. Basia held her breath. - Did you hear that? - Someone's opening from that side - Marcel moved half a step away, but not enough to lose his view. - Or something is breaking down. Lena lifted her gaze. A new Wi-Fi network appeared on her phone screen: "Class-0". The signal was strong, as if the router was right outside the door. Basia looked at her screen. It had the same thing. - 'Don't connect,' she said quickly. - 'Don't connect without the password. The reader flashed green. The door vibrated. It was barely a few millimetres, but they felt a blast of cold air that brought with it the smell of wet concrete and something else - grease? paint? - as if the world on the other side was frozen another day than theirs. - Hello? - dared Marcel. - Is anyone there? In reply, Lena heard something that was not a bell, nor was it an ordinary sound. It was as if someone, very close by, had called her name - as lightly as the trembling of a note that could no longer be stopped. And then the door moved a second time, this time more distinctly, as if an unseen hand had just grasped the handle from inside.