Holmes and Watson return from Manor House to London by train and discuss the recently uncovered crime and the death of a certain Lord Huxley. At home, Holmes receives a letter from his older brother Mycroft, an employee of the Foreign Ministry and a member of the so-called Diogenes silent club; in a letter he asks for a meeting. Holmes notes that Mycroft is endowed with the gift of deduction, with which he skillfully reveals crimes, much stronger than his brother. The meeting with his brother takes place in the Diogenes club, where conversations are forbidden, but in a special room for guests where you can talk. Mycroft gives a letter to a certain lady Eva Brackwell, in which she asks to get rid of the machinations of Charles Milverton - the most vile criminal in London, a blackmailer and extortionist. In the days of Puritan England, Milverton got the correspondence of married women with lovers and offered to buy them for a good amount. Over the years, the blackmail king has acquired a mansion with guards and staff, as well as respect in society. Now he is planning to destroy Lady Brackwell. While the conversation is in progress, Price marker is watching Holmes and Watson from the street. Charles Milverton, informed that Mr. Holmes will protect Lady Brackwell, pays a visit to the detective and reveals to him all his dark deeds, including the death of Lord Huxley, who died after reading ill-fated letters. After an unsuccessful attempt to search Milverton, Holmes kicks out a scoundrel. The only way to fulfill the lady’s request is to rob Milverton and destroy all incriminating letters. Thanks to his excellent ability to make up, Holmes gets to Milverton as a tinker and reveals all the weak points of protection. At night, Holmes and Watson penetrate his estate, but they leave evidence on the way: Holmes, carving a castle on a glass door, leaves traces of his blood, and Watson - traces on the floor, which he unsuccessfully tries to reduce. In the office of Milverton, Holmes finds a box with letters, but, sensing something was amiss, hides with Watson. The blackmailer comes to the office and reads a certain encryption. Under it is written a monogram of four swords in the form of the letter “M”. A lady comes to Milverton, and he decides that this is a servant who wants to discredit the mistress. But Lady Huxley turns out to be a guest - another victim of his fraud. Huxley kills the king of blackmail and, taking the encryption, leaves, and Holmes and Watson, who have actually become witnesses, burn letters and also leave. They manage to escape from the servants, but the gardener manages to pull off the shoe that climbed over Watson’s wall. In the morning, Holmes receives a letter with threats and a monogram similar to the one in the encryption, and notices that the marker is watching them. The police find out about the murder of Milverton. Watson barely manages to burn the second shoe when Lestrade visits them. The inspector asks Holmes to help in the murder case, but the detective refuses to investigate the murder of a scoundrel and a villain. Lady Huxley, whom Holmes and Watson pay a visit to, declares that the monogram is unfamiliar to her, but subsequently sends Holmes an encryption.