The sought-after geophysicist Dr. Leonard Gehra in his birthplace Buchenrode in the Harz Mountains. Although his mother still lives there, he has not been in the mining region on the former German-German border for a long time. Now Leonard is supposed to help save Friedrich Trnitz's unprofitable mine. The boisterous boss, respected by his men but also feared, thinks little of the idea of his colleague Kathrin to search for silver in disused shafts with Leonard's high-tech robot. Above all, he doesn't want anyone to break into a tunnel under the Hohberg that has been closed for decades. Leonard set to work with mixed feelings, because this is exactly where his father died during the GDR era. When he realizes that something is wrong with the story from that time, Leonard is determined to find out the truth. He suspects the key to this from Trnitz and his mother. In his search, he faces some surprising and painful discoveries.