Here is the 6th film in the row about the junior Olsen Gang. This time the Junior's are searching for a treasure that has been missing since the famous robbery of the Norwegian National bank in 1835. The boys have found a secret map, and this takes them to the old town of Fredrikstad, where Egon learns that both his father and unknown grandfather were thieves and that his family being thieves goes all the way back to Ole Høiland, the famous master thief who robbed the Norwegian National bank. Egon and his friends set out to find the hidden treasure. But other people also know about the treasure, and would very much like to put their hands on it first…