Around the time that the chief of police is elected the Most Popular Citizen of Valleby, a thief and impostor is released after two decades in jail and returns to the town with a revenge plan in mind.

The sleepy little town Valleby is getting ready for the cafe owners Dino Panini's and Sara Bernard's wedding, and our popular young detectives Lasse and Maja stand ready to ensure that nothing will go wrong. But when the wedding couple's respective relatives arrive, they prove to belong to rival mafia families.

As people in Valleby are looking forward to Valleby Day, a thief suddenly strikes and carries out a series of thefts, leaving behind symbols linked to the Zodiac and space.

On the eve of the annual Valleby Games, the competitors are injured one by one. The clues lead Jerry and Maya to a dark secret and an old myth about the games' mascot that is said to haunt the hall. Will Jerry and Maya find the solution before anyone else gets hurt and will their friendship survive the trials?

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...

It's late summer in the small town of Valleby, but the calm is disrupted by bad news. The police station is under threat to be closed, which neither Lasse, Maja nor the chief of police wants. They must find a way to solve the situation.

Lasse and Maja find an old mysterious coffin that turns out to belong to the eccentric family von Broms. A centuries-old family fights flare up again and suddenly the coffin gets stolen. Who wants to steal it and why?

Lasse and Maja have had their detective agency shut down by the police chief when a customer ask for help to prove her father is innocent of the train robbery he was convicted of. Lasse and Maja now see their great chance to show off.