Lübeck, 1390. In the capital city of the Hansa League, the gruesomely executed body of a stranger is pulled out of the Trave River. Who is this mysterious stranger who seems to have come from far away? What was his purpose in travelling to the North? And why did the murderer try to keep the identity of this unknown man secret? When his apprentice is accused of the murder, the gruff patrician merchant Rungholt – a man with a relentless toothache and a yen for Hamburg beer – suddenly finds himself involved in a dark intrigue once again. He has only a few days to prove the innocence of his apprentice and recover the honour of his business.
Rungholt soon finds out that the nameless deceased has created strange drawings and maps and possessed books written in an unknown, blasphemous language. A heretic, Rungholt’s patrician friends in the Lübeck city council suspect. Rungholt, however, discovers that the stranger was a scholar from the Orient, an Arabian mathematician and surveyor in the service of a fur trader, here to assess the possibility of a canal between the Hansa cities Lübeck and Hamburg. Such a canal would make the dangerous – but lucrative – passage of the Hansa ships around Denmark unnecessary. But before Rungholt can question the Arab’s employer, this man is murdered. What’s worse: Rungholt, while trying to prevent the murder, himself becomes a prime suspect.