A Murder of Quality is John le Carré's second novel. It features his signature character, British spy George Smiley — but it is not actually a spy novel. It was published in 1962.
Smiley agrees to look into a bizarre letter a friend received at her magazine; the writer alleged that her husband was going to kill her. Smiley's friend is concerned but doesn't take any action, and the letter writer ends up dead. As Smiley prods around in the town, a local boy is also mysteriously killed. Complicating the matter for Smiley is that he's on his estranged wife's turf, which affects how people in the town treat him.
A Murder of Quality is a good, though standard, murder mystery. It isn't really a spoiler to say that the crimes are solved in the end.
The Wikipedia article about the book notes that this is the only novel in which Smiley appears outside of the espionage community. Le Carré has written other books that have nothing to do with spies — The Naive and Sentimental Lover, for one — but they don't involve Smiley.
By the time of A Murder of Quality, Smiley has already appeared in Call for the Dead. The novel uses le Carré's original timeline of Smiley's backstory, which has him about 10 years older than he would later be in Tinker Tailor Soldier Spy. The novel also references his marital difficulties with his wife, the Lady Ann Sercombe. Ann's hijinx are a major plot device in Tinker Tailor Soldier Spy and her on-again-off-again approach to George is mentioned in most of the other books that feature him as a main character.
A Murder of Quality was adapted as a TV movie in 1991. It starred, among others, Denholm Elliott as Smiley as well as a very young Christian Bale. It was also adapted as a radio drama as part of the BBC's series of all the Smiley stories, with Simon Russell Beale as Smiley.
TV movie at the IMDB