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.

A young woman lost her memory after an accident. In the woman's bag is a note with Holger's address, does Holger know who she is?

Mortensen is inconsolable, but Esmé suspects that everything is not right. Together they travel on an adventure round Europe.

The search for Holger continues. Mortensen's hunt continues over the high peaks of the Alps and through verdant valleys. Esmé and Mortensen face unexpected challenges and find it difficult to get along.

Holger makes contact with his young relative Flora Graaf.

Mortensen has stolen Holger's identity for the geographer's great desert conference in Windhoek, Namibia.

Flora and Mortensen meet an American geographer who gives them a dangerous mission.

Mortensen and Flora make their way to the coast of Mozambique with the mission of finding the mysterious treasure.

Flora and Mortensen look for Geografi Graaf's assistant Ravi.

Flora and Mortensen are welcomed by Ravi. They hope to get answers to any questions they have about the mystery.

Flora and Mortensen head to Australia and the remote island of Tasmania's temperate forests and rivers in search of the secret cave.

Flora and Mortensen get a ride out to sea with a lobster fisherman off Tasmania.

The black sun follows Flora and Mortensen and it becomes a wild chase through the coniferous forest and into a wild rapids below the Rocky Mountains.

Our heroes get tied up and left in a barn.

Flora, Mortensen, and Esmé head south to find the Black Sun's headquarters.

Flora does everything she can to save her friends and defeat the powerful Brotherhood of the Black Sun.