Lena got up exceptionally early that morning. She felt as if she had been preparing for something important for a week. She stretched lazily and immediately reached for her toothbrush. She liked this moment of the day - for a moment the bathroom belonged only to her. She carefully brushed her teeth with the almond-mint toothpaste, just as her mother had taught her. As she looked at her teeth in the mirror, the thought flashed through her head that something was going to happen at school today. She was not wrong. At break time, Lena met Oliver, her best friend. He, too, looked like he hadn't slept all night. "You need to see something," he said in a whisper and led her towards the school bathroom, which they thought no one had looked in for years. The door creaked open and a strange smell, reminiscent of a mixture of toothpaste and black tea, reached their noses. It was dark inside, and indistinct handprints shimmered on the mirrors. On one of the washbasins lay a .... a toothbrush they had never seen here before. It had blue bristles and a handle embossed with the letters: "B.Z.W." Oliver bent down and took out a puzzling notebook from under the basin, complete with stickers of teeth smiling in a strange way. A ray of light shone through the window and fell right on the first page of the notebook. There was a drawing of a strange labyrinth - it resembled the inside of a mouth. Reflections of light appeared on the bathroom walls and Lena felt that they had just found something completely unusual. They both sat on the cold tiles, analysing the notebook. Then a quiet bubbling came from the pipes under the sink. Oliver suddenly froze - as if something had emerged from under the floor. Lena tightened her hand on her newly found toothbrush. Suddenly, all the mirrors shimmered and a luminous inscription emerged: "Only a really clean smile has the power to protect the passage...". At the same moment, a quiet clatter sounded behind their backs. Lena and Oliver looked at each other in disbelief. They had no idea what was waiting around the next paste-shiny corner of this old bathroom....