Nostalgic detective story (Russian Edition)

During a picnic body of dead man was found on suburban estate of Russian oligarch Zvyagin. Old house is just recently bought by Zvyagin. Police starts investigation. Who is the victim, why he is killed and who is the murder? Narrow circle of estate visitors compels police inspectors to enter all picnic participant names into the list of suspects . How it is possible to reduce quantity of suspects? Why the diary containing records from the Second War is detected close to the victim body? Is murder connected to other crime illegal, double sale of Zvyagin s house?