Nothing particularly interesting has ever happened at Archimedes High School. Well, except for that one time when the headmaster had his bicycle painted pink, but that has been forgotten by now. The day started as usual: the bell ringing, hands clasped together out of boredom, breakfasts hidden under desks and stares saying "does anyone know what this lesson is about?". It was a Tuesday when he - the new chemistry teacher - entered the school. His name was Professor Eugene Wymyslek. He had hair sticking up at odd angles and a jacket that looked as if someone had fashioned it from the remains of a kitchen cloth and an old curtain. He entered the classroom, looked at everyone and... instead of introducing himself, took a rubber duck out of his briefcase. "Good morning, ladies and gentlemen! Today's lesson on non-obvious reactions. This is Kazik. Kazik is my assistant. Please do not disturb her." The whole class froze. Michal and Lena, best friends since first grade, looked after each other with wide-open eyes. Their bench, always third from the window, trembled from their suppressed laughter. The professor walked over to the table, poured a flask of pink liquid (no one knew where he got it from), placed a rubber duck in the middle and announced: "We are proceeding with the experiment." Kazik, to everyone's surprise, began to... move. The teacher did not have time to react to this at all, because he had already taken a bag of sugar out of his pocket, dropped a teaspoon into the flask and.... something like confetti burst from the flask! The whole class became overgrown with pieces of paper, and Kazik slid off his desk. Michael was sure he was dreaming. Lena giggled louder and louder. The professor looked at them over his glasses and, lowering his voice, asked: "Who can guess why Kazik is running away?" Before anyone could answer, Kazik, or the rubber duck, rolled under the door ruler at the speed of light and... disappeared into the school corridor. At the same moment, a cold pigeon crashed through the window, pushing a mysterious purple letter onto the window sill.... Everyone turned their heads. The letter shimmered and made a strange buzzing sound. Michael and Lena felt that something special was about to begin. But should they pick up the letter? And what if Kazik didn't return from the corridor?