A terrible incident at an old mansion shocked the city of Treverberg. A young woman and a man were found dead—their bodies burned on a bonfire. Young detective Axel Green takes on the case and discovers that it isn’t the first time murders of this kind have happened. The suspect chooses his victims using a strange criterion—always a pair: a young woman and a middle-aged man. Now the detective must solve this riddle and find out who is behind these awful crimes.