In the school cloakrooms of the Number 13 School Complex, an old saying circulated: "Whoever finds a pair wins fate!". No one knew where it came from, but everyone knew the meaning - socks at this school disappeared faster than sandwiches at break time. Julka, Bartek and Aga - the infamous record holders in terms of sock losses - decided to act. They founded the Lost Socks Club and on their very first day of activity, the whole class handed them a stack of applications (and an even bigger stack of individual socks). The club's headquarters were set up in the old cloakroom under the stairs. The caretaker sometimes locked the brooms there, so they considered it a strategic location. They equipped themselves with handy notepads, a detective torch (borrowed from Julka's little brother) and.... a suspicious amount of powdered soups, because "every night action has to have a supply of energy". Already on the second day of the investigation, they came across their first clue: at the end of the corridor, exactly where no one ever cleaned, there was a single scarlet sock with a disturbingly long label. A subtle smell of cheesy popcorn wafted over it. As Bartek tried to pick it up, Aga's voice came from around the corner: - 'Guys, there are footprints here.... and not just any kind! - she whispered excitedly. They followed her towards the football team's changing room. The door was ajar, and an eerie grunting could be heard from inside (none of them had the courage to ask if it might be the director, who sometimes dozed off on the bench after a match). Julka turned on a torch and the light fell on a pizza carton lying under the bench and something that looked like a mechanical robot leg. - 'This is no ordinary day,' whispered Bartek. Just then, the cloakroom door began to close slowly behind them, and there was a quiet, metallic clatter in the darkness. - 'Someone else is here,' Aga said quietly, tightening her grip on her notebook. Everyone held their breath, staring at the mysterious silhouette emerging from the shadows....