A painting worth SEK 22.2 million has been stolen from the museum. Lasse and Maja get to handle the investigation. Barbro Palm goes on a laughing course and suspects an international league.
Mohammed Karat suddenly wants to turn the three wise men into gold hunters. The priest has an outburst of rage and the police chief gasps hysterically that Valleby has turned into an eldorado for thieves and bandits. Lasse's fever rises.
Café Marsaan has been robbed and not just once, but twice. The police chief promises to get a hold of the robber story once and for all, but nothing happens. Then Lasse and Maja decide to catch the robber on their own.
The police chief suspects the night watchman Krister Lönn, and when Lasse and Maja spend the night at the museum, a desperate cry for help is suddenly heard.
Lasse and Maja have started a detective agency. They seek out the Chief of Police who explains to them that December is the quietest month of the year. And just as they talk so is he receiving an alarm from Café Marsaa.
Lasse and Maja takes a vacation. They have a good time at the market that has come to town. A shady elf appears and warns them of pickpockets and before Lasse can say ice princess he is robbed of all his Christmas present money.