The son of a diplomat, twenty-five-year old Mathias Barillet is taking classes in forensic medecine. He lives in Germany, where his father now works, but the boredom of living in Aachen drives him to set out for Paris. During a duties check on the train back to his homeland, Mathias meets a man who threatens and insults him, then simply disappears. The next day, still upset, Mathias discovers a skull in his luggage, a shrunken head, in keeping with Jivaros Indian tradition. Fascinated by this fragment of human remains, he feels somehow responsable. Who was it ? Who gave it to him? And why ?...