Monsieur Lecoq of the French Sûreté is tasked with unraveling a complex bank robbery that has baffled the authorities. The investigation plunges Lecoq into a world of deception and hidden motives, where the lines between victim and perpetrator blur. He must navigate the intricate social strata of Paris and confront a cunning adversary who operates from the shadows, all while adhering to the strict protocols of the Sûreté.

As one of the foundational texts of detective fiction, "Blackmailers" (often known by its original title, "Monsieur Lecoq") is recognized for its significant influence on the genre. Its intricate plot and the character of Monsieur Lecoq are frequently cited as precursors to later, more famous detectives. The novel's detailed approach to crime-solving and its exploration of criminal psychology set a benchmark for subsequent mystery writers. Its enduring legacy lies in its role in shaping the conventions of the detective novel, making it a key work for understanding the genre's evolution.