Holger Nilsson meets the temperamental engineer Mortensen. Together they set out on a raging treasure hunt through Sweden to find the seven keys to Mary Diana Graaf's mythical laboratory.

To solve the riddle, they hike across the Varaslätten and climb one of the country's highest silos. From the steamboat they see the fields of Västergötland. They fly over Skåne, wander through beech forests and over miles of white beaches.

To solve the riddle, they ride a raft on Sweden's largest river and cable car over waterfalls. From Värmland, they travel by dog sled through Norrlands and endless pine heaths where the taiga is preserved and the great forest is untouched.

To solve the riddle, they follow the Norrland coast. They drive through the breathtaking landscape of the High Coast, become shipwrecked on the island of Högbonden and climb high up to Slåttdalsskrevan.

To solve the riddle we follow Holger and Mortensen as they wander through the great Alvaret on Öland and Visby on Gotland, they wander among narrow alleys and see ruins from the Middle Ages.

To solve the riddle, Holger and Mortensen go to the mountains in Dalarna, where Sweden's highest waterfall, Njupeskär, is located. They also visit the mine in Kiruna and hike the Kungsleden down towards Sarek and Rapadalen.

To solve the riddle Holger and Mortensen kayak through the Stockholm archipelago. They sail with an old pilot boat and visit Sweden's westernmost islands, the Väder Islands.

In the final episode, Holger and Mortensen visit Sweden's three largest cities and their most famous buildings and places in order to finally solve the riddle.

Holger discovers mysterious notes in an old geography book that lead him to Oslo and an enigmatic key.

Holger is finally reunited with his old friend Mortensen.

Holger and Mortensen continue their journey and meet a mysterious man in a lighthouse.

Newly found clues lead Holger and Mortensen to southern Norway. Mortensen is doubtful if he still wants to be involved. Holger realizes that they are not alone in searching for the map's secret.

Holger and Mortensen have arrived at Borgund's stave church. There they find another part of the map with another riddle that takes them further north.

From the Finnish forests, Holger and Mortensen make their way to the North Cape. During a joke, Holger sees that they are in the wrong place.

Holger and Mortensen are on Svalbard, almost as far north as you can get. In an abandoned mining town, the pursuers catch up with them, and they are forced to flee.

While Mortensen is recovering from his injury, the old woman Sirpa decides to train Holger to become a master geographer. With Sirpa's echo and newfound strength, they make their way south through Finland's vast lake system.

After the Brotherhood of the Black Sun steals the map, Holger and Mortensen learn that Mary Diana is on an island. Instead of aiming to take the map, they try to find and save Mary Diana.

Holger travels to Iceland to try to reach the place where Gjallarhornet is supposed to be before von Troppeln. Holger reaches the large and terrifying lava area of Dimmuborgir. Here the final battle will take place.