Private detective Alexander Shibaev has never had such clients before! Alois Moltke, a descendant of emigrants, wrote to him from Germany with a request to find relatives and memorable places associated with his family. Moltke’s ancestors were famous people in the city in the past; there were many legends about them, the main one being about a large diamond of an unusual purple hue, which disappeared without a trace. In search of information, Shibaev went to the city archive and discovered the body of a strangled employee - precisely in the department where the documents he needed were kept. Is someone really searching in parallel with him, but clearly pursuing some of their own goals?