If anyone claims that Mondays can't surprise, it means they've never gone down to the basement of our primary school No. 11. There, under the music room and the teacher's office, where the echo can sing better than the choir, is the Archive of Lost Things. Not the usual kind. Ours has seven-page rules and regulations, its own receipt printer and a cat in a reflective waistcoat. My name is Nina, I'm fourteen years old and for the past week I've been managing the blog Escape from the Bell. I haven't escaped once yet, but the title attracts readers. My best friend, Leon, claims to have been a compass in a previous life because he always finds objects by accident. In practice, this means that he has pockets full of other people's pens, individual headphones and hair elastics that, under unknown circumstances, have turned into bungees for pencils. On Monday, he brought a sweatshirt with a pocket so big it could serve as a hamster shelter. - Someone had lost it in the cloakroom. 'The cardigan of the Force,' he announced with seriousness, as if he were rescuing a museum exhibit. - We'll give it back. I'm collecting pluses for karma. - 'Why don't you give away your whole backpack straight away,' I muttered, looking at the notebook with 'PE' written on it sticking out of his inside pocket. - It's not yours. - This one actually is. See the signature. - He stroked the cover. - A page had torn off. So we descend the stairs to the minus-one level. At the bottom we are greeted by a plaque made by Mr Opara, our conservator: "Archive of Lost Things? Please keep it quiet". Underneath, someone has written in pen: "And no harm to mops". Mr Opara was obsessed with mops. He invested in them like a stock. Inside, it smells of dust, old paper and a hint of orange. It's a 'Motivation' scented candle that sits next to a rack of hats. The shelves stretch in long rows. Each has its own category: "Loner socks", "Keys for nothing", "Notes that will come in handy anyway", "Water bottles, but definitely yours". A sticker printer purrs in the corner: BASIA - Base Training and Accessory Inventory Assistant. BASIA doesn't like people. At least that's according to Mr Opara, who secretly loves her. - Hello, BASIA," says Leon cheerfully. - I have a fresh sweatshirt for the catalogue. The printer grunts (really) and words appear on a narrow tape: "Good day. Please do not talk to the machine. Category: Blouse. Colour: Grey. Fragrance: Unwashed. Mood: Medium motivated." - That wasn't nice," I state. "Note user humour: ironic. Assignment: Rack B-5 - Outerwear that someone will be cold in later." - Look," Leon pokes me. - They've changed the layout. Indeed, something is different. A new aisle has appeared between the hair elastics rack and the 'Clips - always two, always separate' box. At its start stand two plastic bollards and an A4 sheet of paper signed by Mr Opara's hand: "Pilot project. Do not enter. Unless stolen time." - Stolen... what? - I crinkle my eyebrows. - Mr Opara and his poetry. Behind the bollards hangs another sign a little crooked: 'Atypical Section'. And underneath, again a BASI print: 'Do not touch shiny objects without sunglasses'. - 'I want to see this,' says Leon in that tone that reworks 'not allowed' into 'this would make a great story for a blog'. We go. It gets cooler between the bookcases. The fluorescent light buzzes like an annoying thought that refuses to let go. Professor Dibble, a cat in a reflective waistcoat, stretches on a cardboard box and looks at us like an air traffic controller. - Good morning, Professor - I bow. The cat rolls over to the other side. His waistcoat glows with the words 'Safety First'. It would be long debated whether this fits the cat. The Uncommon section is small, but rich in impressions. The shelves are labelled in a surprising way: "Watches that make lessons late", "Home portals to the unknown-where-damaged", "Unidentified keys to identified things", "Things that get stubborn". And a table in the middle, and a card on the table. Not the usual plastic library card. This one is metal, thin, matt, embossed with the words: "Pass 7L - Yesterday Only". As we take two steps closer, the card vibrates slightly, as if it were a karaoke record in a treble clef. - Yesterday? - Leon looks like he's just won a voucher for free waffles. - This might be the best spoiler of the story. - Or the worst - I remark, but my eyes are already shining. - Why would anyone need a pass to yesterday? BASIA grunts louder and lets out a bar of text: "Attention. Object class: Lost=Dangerous. Curiosity: Pick up with caution. Recipients: Students in grades 7-8 - categorically no." - This is precisely the most beautiful word in the Polish language, says Leon with devotion. - "No. It always leads to adventure. Professor Kłębek raises his paw, as if raising a doubt. 'I have quite a few of those too. But the card lies and pulses slightly at the edges, and there is a smell in the air, as if someone had opened a jar of yesterday's air after a storm. We can smell it, both of us. - Good - I sigh. - Let's touch, but gently. And if it starts playing disco polo, we run away immediately. - It's settled - says Leon. I touch first. The card is cool, although here in the basement it should be the other way round - everything is always a degree warmer than it should be. I feel a slight vibration on my fingers. As if someone is sending Morse code, only in a version: "Don't panic, not yet". A reflection of light flies over the card. The inscription "Only yesterday" brightens for a moment. - 'Oh, look,' Leon points to the wall behind the table. Only now do I notice a steel door like the one for the school file archive, with only one detail. Instead of a handle, it has a narrow vertical socket, perfectly like under our card. Above the socket - a plaque: "Yesterday only. Access restricted. Use: technical only". Someone has added in pencil: "Technically we are curious". - Better bring Mr Opara," I said, more to sound reasonable. - 'Better bring patience training later,' Leon replies, and does that smile of his that looks like 'trust me', even though the statistic says it's 'we're about to land in trouble'. - Before you press anything... - I add quickly, as Leon is already holding the card - let's check the rules and regulations. The rules and regulations hang nearby in coloured document shirts, like artwork from the technical circle: "Point 1: Found? Give it back. Point 2: Don't test on yourself. Point 3: If something glows, turn off the light and run away." - 'It doesn't glow,' says Leon, who has apparently decided that 'pulsates' is not the same thing. - And I'm not testing on myself. I'm testing with you. - Excellent - I say dryly. - I've always dreamed of being a second-class guinea pig. BASIA lets out a series of squeaks and prints hurriedly: "Warning: Time is a sticky material. Don't get dirty." Then another: "Mr Opara returns in 11 minutes. Please don't do anything stupid for 10." - 'We've got nine minutes,' Leon counts carelessly and, slipping the card into the slot, adds: - At the most, it won't go in. Don't let the 'highest' fool you. At our school, 'highest' almost always means 'oh dear'. The card enters smoothly, as if it has been waiting for this moment all its life. The door makes a sound that I can't attribute to any normal lock. It's something between a sigh and the crash of waves breaking on the pier. For a second, I have the impression that this basement really smells of the sea, even though we are two hours away from the Baltic Sea by train. The fluorescent lights twinkled. Professor Kłębek sat down. BASIA started printing so fast that the tape curls up on the floor like serpentine after New Year's Eve. Words jumped on the narrow strips of paper: "CANCEL", "CLOSE", "NOT NOW", "WAFFLE RECIPE (ERROR)". - Do you hear? - whispers Leon. I hear. Behind the steel door, very quietly, as if from down a long corridor or from the other side of a dream, someone is talking. Two people. One of them is laughing - with a laugh that sounds all too suspiciously similar to mine, only in a slightly lower voice, as if I have a cold. The other responds in an impatient whisper: - They are going to be late by... five minutes. As usual. The pulse of the card next to my hand speeds up. Leon looks at me with wide-open eyes. The door makes a minimal, almost imperceptible movement, like a blink. - 'Maybe we should wait for Mr Opara after all,' I say, but I don't move my hand away. Not because I'm being brash. It's just that there's something about it that works like a magnet. Like an uneasiness that is at the same time excitement. - 'If it's us,' Leon says quietly, pointing at the door with his chin, 'then maybe.... He doesn't finish. Because suddenly, with a blip of light on the 'Yesterday Only' sign, a quiet click is heard, the locks inside groan like a six o'clock alarm clock, and another voice sounds from the other side, this time clearly: - Ready? The door vibrates and begins to slide open