The rain pounded on the large windows of the old high school as if trying to play an impatient drum on them. The smell of wet chalk mingled with that of oil paint and polish, and in the glass cases in the corridor stood leaning cups on which dates from decades ago were engraved. On the wall near the entrance hung a portrait of the patron saint - a stern Erasmus in a black biretta - who, according to the pupils, could stare in such a way that a person began to straighten his back without being asked. Kaja walked fast, although she was seemingly in no hurry. Her backpack whipped around her hip, the sketchbook inside clattering rhythmically against the bidon. Third grade meant out-of-the-box projects, scholarships, portfolios and the whole big, awkward package labeled 'future'. She liked things that didn't fit into a simple timetable. That's why when the e-journal sent out a notification of extra extended physics in room 213b, she snorted with laughter: the numbers in that wing jumped from 213 straight away to 214. 213b didn't exist. - Did you get that too? - Maks joined her by the stairs, twirling his drumsticks in his fingers. He did not part with them even in the library, which regularly made Mrs Grodecka sigh theatrically. - 13:13, room 213b. 'Sounds like an IT joke,' Kaja replied, glancing at her phone screen. - 'Unless someone decided to check on us. - Dr Radecki - whispered Maks dramatically. - Apparently he came from the polytechnic, doing some twisted projects in optics. And yesterday he said he was going to teach us 'spatial thinking'. I don't know if I should be scared. In the lobby on the ground floor there was a big round clock - an old one, with convex glass and black hands. For as long as Kaja could remember, it had been broken. It had stopped a long time ago at 1:13 p.m. and had served as a decoration and a joke for the freshmen since then. That morning, however, the hands vibrated. Barely, almost imperceptibly, but they twitched. Someone noticed it - whispers spread like a wave across the shallow waters. - Look - Maks nudged her with his elbow. - 'Either I think it's me, or that corpse just blinked. Kaja stopped under the clock, feeling her own heart adjust to an inaudible tick-tock. For a moment, the world narrowed to a circular dial and the reflection of a lamp in the convex glass. Then someone poked her in the back and out of the jumble of voices emerged the school bustle: timetable, bells, tests, someone lost a pencil case, someone running to film circle. The library smelled of dust and tea. Mrs Grodecka, a librarian with a beard twitching at every "good morning", looked after not only the books, but also the files of plans and engravings depicting the history of the building. The high school stood on the site of a former villa with an orangery, then a wing with a gymnasium was added, and somewhere above it all hung a history a little too serious for a corridor with posters about a biology competition. - 'Mrs Grodecka,' Kaja began, leaning with her hip against the lending library countertop. - Do you have a plan of our school? The older one. I'm looking for room 213b. - Dear child - the librarian rolled her eyes, but she was already reaching for her folder. - 213b is not there. There used to be a second 213 because they got something wrong with the numbering, but that was years ago. Then they bricked up the passage because it made a draught. Why do you need it? - The e-journal says we have physics there today," added Maks, placing his chopsticks on the counter, as if in deposit. - 13:13 - such... symbolism. Mrs Grodecka stopped in mid-motion. She looked at them in a different way, as if she finally saw not only backpacks and thermal cups, but also two curious heads. She pushed back the folder, took out a yellowed technical drawing. - It was a plan from before... hmmm... the seventieth. They added the north corridor then. Look - she pointed with a pencil to a thin line between rooms 213 and 214 - There's an alcove here. Except that access was from the other side. Apparently they used to keep physics models in there. And then they made it into a storage room. Or not. Nobody likes to open a door behind which it blows. - Blowing? - repeated Maks with perverse curiosity. - Figuratively, Maks. And a little literally. The old walls like draughts," cut off Mrs Grodecka, but she was already writing it down on a piece of paper: North corridor, next to the display case with the chess medals, behind the announcements. With the bell ringing for the third lesson, Kaja stopped thinking about the building plans. The Polish teacher told her to write a short scene with an inversion, the meaning of which changes with the point of view. Later, biology, a short test on mitosis. Then a break, coffee from the vending machine, a quick chat with Zosia from the school radio, who already knew about the 'waking clock' and was planning a feature. Kaja liked this rhythm: circled, nervous, lively. And yet, every few minutes, her thoughts returned to the thin line on the set and the promise of something knocking just a whisper against the wall. At the long break, they returned to the chess players' medal display case. There were school posters hanging at the back: choir recruitment, an exchange with Barcelona, an ad for a lost cap with a red pom-pom. Kaja slid her fingers under the edge of the frame and moved it slightly. The whole structure squeaked and swung open like a door, revealing the narrow grey plane of the wall. At hip height, the outline of a rectangle could be seen - an old, bricked-up passage clad in plaster, on which time had left a map of cracks. - 'This is the moment when the wise man goes to the canteen,' Maks stated. - And the curious one looks for a soup spoon to pick at the wall. - The canteen today has croup. The wall won," muttered Kaja. She moved her hand over the plaster. In one of the cracks she sensed a chill and something metallic. - There's a hinge here. Only... mudded. A sudden silence joined their creaking. The corridor on the other side of the turn was silent, as if the whole high school had taken a breath of air. The realisation that they were doing something between 'slow' and 'not slow' made Kaji's heart quicken. Ever since she was a child, she had hated lying, but she was drawn to see where closed doors led. - Move that notice board,' she whispered. - Like... yes... by a centimetre. Then they heard a sound that pierced them inward. The clock in the ground floor hall - the one never repaired, with the convex glass and black hands - struck. One time. A second. A third. And then a brief silence hung in the air, as if someone had closed a book just before the last paragraph. - 13:13 - said Maks half-heartedly, without humour. Something twitched in the crack in the plaster, as if the wall had taken a shallow breath. Kaja withdrew her hand and felt that her fingers were white from dust. Then, very slowly, a thin scrap of paper slipped out of the same crack. Like a letter that someone from there was pushing through with quiet determination. Maks turned into a statue. Kaja grabbed the edge of the piece of paper, carefully. On top, in smudged pencil, someone had written today's date. Below that, three words: "Kaja, don't be late". Her name was written in a handwriting she knew all too well - her own. - 'No,' she whispered, feeling the cold pass through the skin on the back of her neck. - This is some kind of joke. - Zosia? - Maks guessed. - Or the one from the technical workshop who can forge anything? Kaja turned the sheet of paper over. On the back, in fog-thin writing, it added: "Room 213b. One entrance. Be before the second bell." - 'The second bell is the break before physics,' said Maks, looking at the screen. - 'In nine minutes. This was no time for discussion. Kaja slipped the card into her sweatshirt pocket, wiped her hands on her jeans and looked around. Behind the display case with the medals was a pillar, and on it was a small, almost invisible handle - a hole in the plaster that looked like an accidental chipping. She pulled. Nothing. She pushed. Nothing. Instead, she felt the handle tremble slightly, as if someone on the other side was holding it in their fingers and waiting for the right signal. - 'I don't know if this is wise,' breathed Maks unevenly. - But if it's a stupid idea, at least it's a spectacular one. Kaja looked at him with a mixture of fear and excitement. In her mind she had diagrams, drawings, a quiet premonition that this could be something on the edge of construction and imagination. The clock was silent. The corridor hummed only with the light of fluorescent lamps. Somewhere far away a classroom door closed and someone snorted with laughter. - 'If the caretaker comes by any minute, we say we're looking for pipes,' whispered Maks. - Or that a history hammock has escaped us. - A hammock? - Kaja snorted, but quickly found her composure. She held out her hand again, more firmly, more confidently. - Good. Three... two... She didn't manage to say 'one'. The lock on the other side surprised itself. The plaster reacted quietly, like a contented old cat. The passage moved a hair's breadth. From the darkness behind the wall came a chill and the smell of chalk, as distinct as if someone had stopped writing on the blackboard a moment ago. And then, somewhere in the middle of this invisible space, something clattered, someone moved a chair and they heard a whisper: Kaji's name, pronounced in a tone she had never heard before in this building. Kaja tightened her fingers on the doorknob and looked at Maks. The man nodded, once, very slowly. Then a dim light flashed in the darkness, like a laser pointer switched on for a second, and stopped exactly at the edge of the passageway, as if to indicate where....