Friday afternoon and school is out. But not for Luca, Ben, and Mina. They have to stay after school, oddly enough in room U1 in the basement of the Leonardo da Vinci Gymnasium. There’s no sign of teachers, just a note instructing them to solve the problem on the board. Mina has no interest in this dusty hole with the flickering light on the ceiling. She wants to leave - but the door is locked. Now, a top-notch puzzle journey begins for the three friends. Who is behind all this? Figuring that out is the reader's task. They must solve the puzzles to find out which direction the story continues. Clues can be hidden anywhere, creative solutions are required, cutting out, drawing, folding - anything goes. And time is running out...