While investigating a rather ordinary case, senior investigator Volin accidentally stumbled upon a cache of old diaries. And there... and there he finds the encrypted notes of the mysterious court adviser X, a genius of intelligence and criminal investigation of the 19th century. On the yellowed pages, a spy story unfolds, in which even the closest person can turn out to be a traitor, mortal danger lurks around every corner, and any mistake threatens to result not only in the failure of the operation, but also in the complete collapse of the entire country... The novel “The Case of Zili Sultan” opens a unique series “ANONYMOUS”, which will include detective novels connected by the main characters and the storyline. The authorship of this series will be revealed only after the publication of the final book. Thus, readers will have to not only appreciate the originality of the plot, but also feel themselves in the role of detectives and unravel the main intrigue: are the works written by one author or did a creative team of writers work on the series?