Primary School No. 27 was of red brick and had a turret on which the wind played its own concerts in winter. On Monday mornings the corridors smelled of chalk, wet jackets and freshly brewed coffee from the staff room. To the left of the main entrance stood a large glass display case with diplomas and the school newspaper. Underneath it, the 5b children always stopped, as gossip spread faster than bells from here. Lena Stawicka, an eleven-year-old with dark hair done up in a ponytail and a perpetual pencil behind her ear, liked to draw plans. She had a rolled-up map of the school in her rucksack, made for art class. Olek Pietras, tall for his age and with a perpetually dishevelled fringe, preferred to construct: he assembled robots out of blocks that could clean his desk better than some pupils. - Do you see this? - whispered Lena as she entered the first break. She stopped in front of a display case. In the middle hung a piece of paper with the words: "Exhibition: our school through the eyes of the pupils". Below, attached with pins, were drawings. One of them made Lena's hand tremble momentarily as she mended her scarf. It depicted the front of the school with a turret, exactly as Lena saw it every day. The caption on the side said: "L.S.". Lena swallowed her saliva. - 'Those are my initials... but I didn't give it away,' she whispered. Olek brought his face closer to the glass. - Maybe someone else has an L.S. too? Lena Sobolewska? Leon Szczerba? - I don't know any Leon,' Lena muttered, then raised her eyebrows. - 'Look at that window on the third floor, on the left. Can you see it? The light's on. - So what? - It wasn't there just now. Olek snorted with laughter, but immediately became more serious, because when Lena moved her finger along the glass, their reflections moved, and the window in the drawing... flickered. As if someone inside had swung the curtain. The pins creaked. A thin, barely visible line appeared under the signature, which Lena was sure she had not noticed there before: "Workshop 13 - open door - today, 2pm". - 'There's no thirteen at our place,' said Olek, with that explorer's tone of his, already hoping for treasure. - The numbering ends at twelve and jumps to fourteen. That's because of the secretary's superstition. - Or... - Lena fell silent as the lady in the green library jumper had just brought new books to the display case. - We'll ask if no one's listening. In Polish, Mrs Seagull, whose name always seemed slightly humorous to the pupils, handed out cards and pens with a feather on the end. She talked about stories, about world-building, about how "details are like grains of sand: whole beaches are made of them". Lena scribbled away, but in her mind she still had a light window on the drawing. After the bell at the second break, the air trembled as if the bell from the turret had rung not two, not three, but five times, although the school bell was electric and always sounded identical. The children scrolled down the corridor and Lena and Olek stood by the evacuation plan and counted the doors. - 'Ten, eleven, twelve... fourteen,' Olek calculated. - 'See? There is no thirteen. - Then what would the inscription be for? - Lena leaned over to see something closer under the display case. The yellow light, which came incessantly through the coloured stained-glass windows on the staircase, moved across the floor like a rainbow river. At one point, the blue triangle stopped just short of the left leg of the display case and turned into an arrow, perfectly aimed at the skirting board. - Did you see? - hissed Lena, feeling a shudder down the back of her neck. - 'That looks like a clue. - Or like a coincidence,' muttered Olek, but he was already kneeling down and looking under the display case. - There's a wheel! On wheels. We can move it. The display case was heavy. It creaked like an old door in the movies, even though it was bolted to the wall. Lena glanced nervously at the crowd of students. They were all busy with sandwiches, guzzling each other's pencil cases and flipping through pages in their music notebooks. The maths lady was standing far away, by the stairs, and talking to the headmaster. - On the count of three - whispered Olek. - One, two... They pushed. First by a centimetre. Then by five. The display case trembled, dust danced in the column of light. Behind it, instead of the usual wall, you could see a vertical crack in the paint, as if someone had once traced a rectangular shape and then painted over it. At eye level, where the door handle should have been, was a star-shaped metal rosette. - 'This is impossible,' Lena breathed out. - There is a ... door here? - Don't tell anyone - Olek lowered his voice. - Let's go get the caretaker. Or better not. He'll say it's the 'archive' anyway and chase us out. Almost at the same moment they saw Mr Teofil, the caretaker with a moustache like a brush, walking down the corridor with a bunch of keys so big that you could ring them to the rhythm of Christmas carols. He stopped beside them, squinted and sighed. - 'And what are you youngsters up to here? - He asked, but there was no anger in his voice, only weariness and what Lena would call a shrug. - Mr Theophilus... - she began cautiously. - Is there a room number thirteen in this school? - There isn't - he answered immediately, all too quickly. - There wasn't and there won't be. At least on the timetable. - He took a breath and added more quietly: - 'There used to be a studio here, as old as my ladder. They closed it down as they were renovating the building. And a good thing, too. Less cleaning. - And what was in this workshop? - Olek asked, feigning an indifference that deceived no one. - Lights, glass, stories... - muttered Mr Teofil and blinked, as if waking up from a dream. - The old teachers collected all sorts of things. I'm going to take the light bulbs to the library. Don't rummage behind the display case. - He snapped his finger against the star-shaped rosette, as if to dispose of it, and went. Lena and Olek stood speechless for a moment. One look was enough for them to agree on a plan: they would return here after lessons, when the corridors were empty. Lena took a thin notebook out of her pocket. She drew a star, a gap, even a bolt that protruded from the skirting board. Underneath she wrote: "2pm - open?" By the end of the day, their thoughts were far from fractions and grammatical cases. In art class, Mrs Seagull asked them to take their easels to the storage room by Room 12. Mr Theophilus opened the padlock for them by rummaging through a bunch of keys, in which each had a different shape. One of them caught Lena's eye: it had a head shaped like a small star, exactly like a rosette. As they handed back the easel and thanked her, the key brushed against Lena's sleeve. It caught on a thin clip from her pencil case. Mr Theophilus had already rushed off to his next errand. Lena unfastened the pencil case and blinked: the star stayed with her, as if unnoticed by the rest. - 'We'll give it back afterwards,' she said quickly to Olek, who only managed to open his mouth. - 'After all, we're not stealing. We're just... borrowing. A little before fourteen o'clock the corridors were deserted. The secretary was closing a window and pouring herself a cup of tea. The stained-glass window in the stairwell cast coloured spots on the walls, dancing and changing. Lena and Olek stood by the display case. The lights in the drawing ... were different again. On the third floor, in the same window, someone painted as if with a thin line waved a tiny hand at them. Lena felt a gentle, cool current run down her back. - Are you ready? - Olek asked, although they both knew it was a pointless question. - 'Sure,' replied Lena and smiled, although her fingers were icy. Together they moved the display case, faster this time, as if the legs themselves knew what to do. The crack outlined itself more sharply in the light. The growing shadow of the turret fell acutely on the rosette, making the star seem to glow in its shadow. Lena slipped her fingers into her pocket and took out the key. It was heavier than it looked and trembled slightly, as if something was ticking inside. She applied it to the star. The pattern fitted perfectly. The lock inside clanked quietly and then clicked, as if no one had looked in it for a long time. At the same moment, the school radio sizzled and a whisper came from the speakers, which usually only gave announcements about lost caps. - 'Please don't come in,' said a child's voice. - Not just yet. Lena froze and Olek looked up at the black eyes of the speakers. The voice was not the secretary's or any teacher's. It sounded like someone they had never seen and yet had known for a long time, like a familiar melody heard in their sleep. - Did you hear that? - choked out Olek. - 'Yes,' replied Lena, and her fingers turned the key of their own accord without asking permission. The lock gave way. The door, which was not on any plan, swung open a hand's width. A cold blue light poured from within, smelling of dust and oil paint and something else neither of them could name. The air lifted the edge of Lena's scarf, and from deep within, in a darker corner, something moved and took a step towards the gap.