Monday at SP12 in Kawonowo started as usual: the bell rang with the tune from kindergarten, the janitor lady Rose shouted not to chase in the corridor, and my backpack decided to pretend to be a black hole. Inside I had a Polish notebook, three sodden chocolate bars and exactly zero pens. Although I had thrown five in there last night - I saw with my own eyes. - You don't lose pens. They run away," Maks said when he saw me digging through my backpack like a sleep-deprived postman. - Where to? - I groaned, rummaging blindly and pulling out a paper clip, a half-printed picture of a cat and a glitter eraser that used to be white and now looked like a meteor. - 'To the place where washing machine socks and my ambitions in maths class also escape,' Maks replied. - Here. - He pressed his own pen into my hand. It was wrapped in duct tape and had a miniature dinosaur glued to it. - Just give it back. This one is happy. I looked at him doubtfully. The dinosaur had a look on its face as if it had just seen the electricity bill. Just then the bell played for the second time, and it was "Ducklings". The students in the corridor abandoned their seriousness and started sniffing behind the dance line. Headmistress Dzierżba leaned out of her office and cast a look that could kill the music. The bell obediently hoarse and fell silent, but I saw her lips twitch. Almost a smile. Almost. - Either someone has hacked the system or the bell is humming," Maks muttered. - 'Or,' I added, 'the runaway pens are back and they're in the staff room, signed 'trophies'. The first two lessons flew by like a sock in the dryer: seemingly there, and suddenly it was gone. In physics, Mr Spike announced a competition: "The most unnecessary, yet working experiment". The grand prize: two tickets to the Escape Room and a pizza for the team. I felt like shouting "I'm in!", but I straightened up just a little more. At the break by the drinks machine, where Coke was never Coke because she always swapped places with Fanta like twins, Maks leaned against the wall and looked at me the way you look when you come up with an idea so good you're afraid to say it out loud. - 'We're going to make a disappearing item detector,' he said in a conspiratorial whisper. - 'So... a magnetometer for pens? - I snorted. - No. Something better. From a walkie-talkie, a tea strainer, an old keyboard and... - he mused - and that torch that flashes blue when the batteries are thinking of retirement. We're going to look for where everything is escaping. If we find the source... - ...then I'll grab a pizza and you'll stop borrowing rubber bands from me. 'I'm in,' I said faster than reason had time to speak, and my stomach decided that pizza was a life goal. We started gathering our equipment. Nika, who usually kept with us on projects, was rehearsing the choir this time and just waved cheerfully, handing me her perpetually tangled headphones. - Like my cat. 'Headphones always come back in one piece, but you'd sooner die than untangle them,' she said. - Good luck, sock detectives! - Don't use that word,' hissed Maks with the look of a mysterious agent. - We are investigators of everyday phenomena. - And strange - I added, because strange liked to stick to us like Velcro to the trousers of Mr WOS. After lessons we sneaked downstairs. "We sneaked" is perhaps too much to say. We simply walked down the stairs to the basement because the door was open and Mrs Rose, with her nose in her crossword puzzles, didn't even look at us. The basement smelled of dust, an Earth Day poster from 2011 and paint that had seen more secret plans than our electronic diary. Sorry: plans. The walls were as green as a lined notebook, scratched in places from chairs that someone had once dragged backwards. A fluorescent light flashed at the end of the corridor, doing a 'pyk, pyk', as if trying to walrus order help. - 'This is where things disappear,' pronounced Maks, looking around with pious seriousness. - Can you smell it? The smell of unfinished projects. - I think it's the paperclips from the static charge - I muttered, but inside I could also smell something... electrical. In a room described as 'Storage - don't go in without Rose' we found shelves full of everything: "P.E. shirts (not lost)", "Artificial pumpkins (a real problem)", "Toner boxes (don't ask)". And shoved into a corner was an old metal cupboard with a crooked door. On the door someone had written in chalk: "FOUND THINGS AND THINGS THAT CAME BACK ON THEIR OWN". Someone added below: "Seriously". Someone else: "I think". - Wardrobe of Rather Found Things - I read it. - I like the 'rather'. It's honest. Maks set our equipment on the table. We took the walkie-talkie out of the box "Trip to the Bieszczady 2008, do not donate to the museum". The tea strainer took its place of honour on the tip like an antenna. I taped it so solidly that if the apocalypse had tape in the range, it would just stick and not come off again. - 'Okay,' he said, pushing the button. - If the theory is right, then whatever 'devours' the pens will 'buzz' in this area. - Your stomach is already buzzing,' I pointed out. - Does that count? Before he could answer, the walkie-talkie beeped. At first timidly, like a mosquito with an allergy to humans. Then more strongly, it wailed and became more and more rhythmic. Pyk. Pyk. Pyyk. - 'Oho,' said Maks, and his eyes lit up like lights on a Christmas tree that don't want to cooperate and suddenly go. - The signal. We're going after it. We moved along the shelves and the device buzzed harder as we approached the corner. Squeezed between a cardboard box marked 'Edible Mushroom Exhibition' and a glue box was a large P.E. bag. One from which something with dots was sticking out. - Wait," I said. - Is that a... sock? It was a sock. Navy blue with white peas, with a neon yellow heel. And it was vibrating. Not the way a washing machine flutters on a spin. Gently. As if it had a phone set to vibrate inside. - Don't touch it! - cried Maks, but of course I had already done so. The sock emitted a prolonged "Wiiiiiii", like a miniature fire brigade siren, and began to glow. Only faintly, with the kind of sad neon, like an 'Open' sign when they're about to close. - Okay, this is officially the strangest thing I've seen today," I admitted. - And today's biology lesson had a film about a slipper. - This is the perfect indicator - Maks stated matter-of-factly. - 'Either they've brought a sock hoover to school, or we've got something that resonates with our detector. The sock will be our... um... calibrator. - What? - I laughed. - Speak normally. Sock shrieks when he's near something that steals pens. - Thank you - he nodded. - Poetically. We attached the sock to the detector with tape. It looked like the microphone of a makeshift punk band. We went through the whole warehouse again. The signal jumped and fell silent, as if it was losing its breath. A mighty salvo of howling only set off the sock at the last door in the corridor, the one with the scratchy 'Cleaning Supplies' sign. The door was ajar, and behind it was a corridor and another door - metal, with a number stuck on crookedly: 13C. - 'This must be here,' said Maks, serious like a news presenter. - A number like out of a horror film for children. Well, beautiful. - At least happy,' I replied, and was immediately corrected by Niki's gaze from my imagination: "Superstition is nonsense, Lena." I pressed the handle. The door didn't even creak, as if it didn't want to overdo it. Inside was a small room with a concrete floor, like a mop and bucket shelter. A metal cupboard stood against the wall, exactly the same as the one before, only with the door closed properly. On a piece of paper stuck with tape was the inscription: "Do not move. Seriously." Someone had added a smile. - It looks like a meme with a warning: "Don't press the red button," Maks stated, and the sock whined approvingly so loudly that I twitched. We put our hands on the cold metal. The walkie-talkie flashed interference. The tea strainer tapped rhythmically against the casing, like a dog against the door because it wants to leave. A hesitation passed through both of us, the kind of brief one in which the brain asks: "Do we need an adult?". The answer was: probably yes. Our stomach: pizza. - For three? - Maks asked. - 'For three and a half,' I replied, as lengthening the countdown adds to the courage. We started: - Once. The sock flashed harder, the neon went into a 2007 disco flicker. - Two. Something knocked from within. Three short knocks. Knock. Knock. Knock. For a split second I thought it was a bucket that had strayed into existence and was asking for a way out. - Three... The handle vibrated in our hands. Somewhere in the corridor, a fluorescent light hissed and went out, leaving only that ridiculous sock neon and the pale screen of my phone, which began to vibrate of its own accord. The display flashed: "Incoming call: unknown sender". A drop of cold air slid across the back of my neck like a vicious icy finger. We took a breath at the same time and pulled the handle simultaneously, and there was a sound from the cupboard that could not be mistaken for anything else - a long, low, metallic swish, as if someone on the other side had taken the cork out of....