Ada has always been curious. As soon as she noticed that there was a strange crack in the bathroom tiles under the old school on Cherry Street, she immediately decided to investigate. Especially since, since the new caretaker Janek had started mopping the floors, there was a slightly minty smell in the bathroom, completely different from usual - as if someone had poured a whole tube of toothpaste in there! That day after lessons, Ada took Max, her best friend from class, with her. Max was sceptical, but his love of adventure was stronger than the fear of punishment from the class teacher. - 'I'm telling you, there's something there! - whispered Ada, pressing her ear to the tiles. - Do you hear that noise? Max knelt down next to her. Indeed, there was a kind of quiet whispering coming from under the floor, as if hundreds of tiny toothbrushes were practising a march. Suddenly, one of the cracks widened and a tile slid aside. Without thinking, Ada slid her hand in and encountered something soft and slightly sticky. To their surprise, underneath the tile was a tunnel - bright green and shiny like a freshly washed glass. Crawling first Ada, then Max, they reached a small cave that looked as if it had been carved in.... toothpaste! The walls shone white and the freshness of mint was in the air. Miniature figures made of gel droplets ran around them - they had toothbrush-like hair and sparkling green eyes. Suddenly, one of the gel folk approached them and said: - You are the chosen ones! Only you can help us save the Fluoride Grottoes from the mysterious Prince Prodigy! Max looked at Ada with horror and excitement at the same time. A moment later, there was a strange rumbling in the wall, and from the depths of the tunnel came a sinister, snarling laughter....