In the dark, chalk-smelling basement of Primary School No. 8, Lena, Kuba and Sara found something none of them expected. It was Wednesday, the last lesson had been cancelled due to a power failure and the kids decided to use their free time to explore the oldest part of the school, shrouded in school stories. Under the stairs, behind an old bookcase with dusty globes, Kuba nudged something with his foot. It was a metal container resembling a coffee can. Lena opened it impatiently and then a huge, yellowed piece of paper appeared to their eyes. Someone had drawn an elaborate map on it a long time ago, perhaps even before the war, with a hall in the centre, signed as 'The Kingdom of White Teeth'. Sara, a walking encyclopaedia, immediately recalled the legends that circulated among the pupils: supposedly there used to be special corridors under the school built by dentists who wanted to teach the children how to take care of their teeth. However, over time, some of the entrances were bricked up and the project was forgotten. It was also said that strange carious beasts lurked in the dark tunnels, coming out at night to hunt for leftover under-cleaned cola and candy. Cuba, always sceptical, laughed nervously: "What the hell, probably some old caretaker's joke." But Lena felt she couldn't let go. "Let's at least leave footprints on the floor so we know how to get back!" - she chuckled, pulling coloured chalk from her backpack. Against the wall, they noticed a small door masked by a hanging poster about brushing teeth. They opened it and froze - there was a steep staircase leading down inside, and a quiet sound came from deep inside.... like the clatter of glass against glass. Kuba threw the torch inside. To their amazement, the light reflected off some smooth surface, and strange white shapes resembling huge crowns of teeth shone on the walls. "Shall we go?" - Lena looked at her friends with a mixture of fear and excitement. Sara squeezed the map tightly, Cuba silenced his phone so as not to betray their presence. Carefully, one by one, they began to descend deeper into the underworld. They did not yet know that with every step they took, they were encountering traps devised by the former guardians of the kingdom - the city's most famous dentists. There was an aroma of mint and eucalyptus in the air, but somewhere, in the distance, a disturbing scrabbling could be heard, as if something was sharpening its teeth in the darkness.... When the torchlight fell on the first strange inscription carved into the wall - "Brush or you're lost". - Lena realised that this was only the beginning of their adventure....