General de Merville's young daughter Violet has fallen in love with the roguish and sadistic Austrian Baron Adelbert Gruner, who Damery and Holmes are convinced is a shameless philanderer and a murderer.

The Baron will not be moved and claims that his charm is more potent than even a post-hypnotic suggestion in conditioning Violet's mind to reject anything bad that might be said about him.

Gruner tells the story of Le Brun, a French agent who was crippled for life after being beaten by thugs after making similar inquiries into the Baron's personal business.

Violet still stands firm, and the meeting ends with Holmes narrowly averting a public scene involving the enraged Kitty.

The next day, Holmes presents Watson with a fake business card styling him as "Dr. Hill Barton" and an actual piece of Ming pottery, a saucer.

As Watson faces his murderous captor, a noise from another room alerts the Baron, and he rushes into his study just in time to see Holmes jump out of the window, having stolen the book.

[3][4] The story was adapted by Edith Meiser as an episode of the American radio series The Adventures of Sherlock Holmes.

[10] An audio drama based on the story, starring Robert Hardy as Holmes and Nigel Stock as Watson, was released on LP record in 1971.

[11] "The Illustrious Client" was dramatised for BBC Radio 4 in 1994 by Bert Coules as part of the 1989–1998 radio series starring Clive Merrison as Holmes and Michael Williams as Watson, featuring Michael Feast as Baron Gruner and Ruth Gemmell as Violet de Merville.

[14] The 1991 Granada TV version with Jeremy Brett is faithful to the original, except that it shows that Miss Winter's revenge attempt on the Baron was because he had disfigured her neck and chest with oil of vitriol, and in the small detail that Grüner finds Holmes inside the house, and Kitty (played by Kim Thomson) rushes inside and past Holmes to throw the vitriol at Grüner played by Anthony Valentine.

In this version, Kitty flees the United States to an unstated destination so as to escape arrest after she scarred Gruner's face with a caustic chemical.

In a later episode, The View From Olympus, Holmes mentions a previous case about a man who killed his wife on the Splügen Pass and made her murder look like an accident.