12-year-old Mariana and her stepbrother Marcus end up in a home-built rocket. Behind the rocket construction are Albert, a slightly crazy scientist, and his helper Lemming, a talking lemming.

The duo from the popular detective series gets their first serious job. The Hammurabi Contest stands a chance of becoming a great event at the school in Valleby. The prize is an ancient book containing the rules of solving disputes. Short before the contest starts, the book disappears in mysterious circumstances. Without the book, the contest will not take place! All the effort and dedication of pupils would be for nothing, and the school would lose its prestige. Jerry and Maja are involved from the very beginning, trying to find the lost book. Will the kids find the underlying cause of the case? A white dove will help them solve the mystery...