High in the Bandiagara Mountains in French Sudan (modern Mali), ethnographer Richard Bellheim in October 1893 discovered a city abandoned for many centuries by the mysterious Tellem people, who arrived in these parts from the Central Sahara. According to legend, these people had amazing astronomical knowledge. Returning to Berlin a few weeks later, Bellheim gives a talk at which Karl Friedrich von Humboldt is present. But, oddly enough, Richard Bellheim no longer recognizes the friend of his youth. Moreover, since the ethnographer returned from Africa, he has changed amazingly—it even seems to have begun to eat glass. Bellheim's wife, Gertrude, begs Humboldt to find out what really happened to her husband in Africa. And so the Pachacutec, the traveler's and explorer's aircraft, takes Humboldt, Oscar, Charlotte and Eliza to the mountains, where they have to find the trace of the Glass Curse...