A story in which two dozen-year-old detectives play the leading role. Will they deal with another mystery? Who is their friend and who will try to prevent the discovery of the truth?

Lasse and Maja, young detectives from Valleby, start another investigation. They will try to find out what a mysterious casket can contain that no one can open. They know that this is a souvenir of the von Brom family. They try to find out what is inside, but one day, not only the mysterious casket disappears, but also the family rings of the von Brom family begin to disappear. How will Lasse and Maja handle this puzzle? Who took the souvenir and can it be opened?

Awards
Golden Fern Flower - audience award in the best film category 2015, Golden Fern Flower - jury's award for participation in the main competition of FF Kino Dzieci 2015.