Student Gerd "Gonni" Gonnfeld is found dead in the Hirschsprung Tunnel of the Höllentalbahn. Initially, everything points to suicide, but then it is revealed: he was murdered. And this happened in a tunnel of the Höllentalbahn, for which Gonni was supposed to write a seminar paper for his history studies. In the same seminar studies Alfred, the former local reporter, who resumed his studies after being dismissed from the newspaper. Alfred's seminar topic is: "Mining in the Middle Ages at Schauinsland and in the Oberrieder Valley." And then there's his classmate Vanessa, who is supposed to give a presentation on the robber knight lineage of the Falkensteiners. Gradually, it becomes clear: the murder of Gonni and the three presentation topics are connected. The key to everything is the mysterious "golden Marti"...