Cuba was sitting on a bench in the changing room and making a very serious face. If it wasn't for the fact that his socks were glowing with stripes like a traffic light, someone would probably even believe him that it was a 'minute of thoughtfulness'. But Anna, his best pal, just rolled her eyes and snorted with laughter. - 'Cuba, after all, you know that if you lose one sock, it's gone,' she announced, waving her own purple heel. - The sock monster never gives up its booty! - You should be more serious, Anna - replied Kuba, trying to hide one leg under the bench. - That's the fourth lost sock this week! After all, I'm going to come to school in two different ones tomorrow, and Mrs Jola is going to ask me again if I only wash them individually at home. Ania squatted down next to him. - What if it's not a monster? - she whispered mysteriously. - What if someone... or something... swallows socks on purpose? Cuba's eyes got as huge as buttons. - Do you think we should check it out? Before he could finish his sentence, however, Philip, their mutual friend from 5B, rushed into the changing room. He was wearing only one shoe and holding the other, with a suspiciously familiar striped sock dangling from it. - Someone had put my sock.... into a sandwich! - he groaned and pulled something out of his shoe that looked more like a pasta monster than breakfast. Anne and Kuba looked at each other communicatively. - 'The matter is getting serious,' said Ania, glancing at the door leading to the school kitchen. - 'We need to have a plan. And we need to get someone else involved... And just then the door to the cloakroom creaked quietly. Mr Leszek, the caretaker, stepped inside, with a face as mysterious as if he had just swallowed a ruler. And under his apron, at the very edge of his trousers, something colourful was showing... a sock, but not an ordinary one, but... with an embroidered inscription: "Do not touch! Threatens to retch!" - Hmmm - muttered Mr Leszek, looking at the children penetratingly. - Who has lost a sock since this morning, hands up? They all hung their gaze on his feet. Because two little socks had just started to romp merrily on the floor.... two tiny sock feet that didn't belong to anyone! Do they dare to find out where these colourful footprints lead? And where do these sock antics come from?