Genteel Interbellum Setting

An unspecified (usually) date somewhere between the end of World War I in 1918 and the commencement of World War Two in 1939. A time of women in evening gowns and gentlemen in dinner jackets mingling at well-to-do cocktail parties, rich tweed-clad country gentlemen and detectives who are veterans of World War I. Lots of action takes place in big country houses and small surrounding villages in the countryside, often involving (depending on the author/genre) either wacky romantic misunderstandings or cold-blooded acts of murder, both of which evolve around complex, labyrinthian schemes. In the more urban areas (usually either London or New York), there's lots of Art Deco around, swank parties, heavy drinking, and gay repartee. While The Roaring Twenties and then The Great Depression both took place around this period, the rather conservative and patrician milieu of the Genteel Interbellum Setting tends to keep the era's real-world social, cultural, and political upheavals somewhat at arm's length.

This trope was formerly named "Christie Time" after the period when most (if not all) of Agatha Christie's Hercule Poirot Novels are thought to be set (they actually cover a time period of 1916 to the early 1970s, suggesting that Poirot lives to be over a hundred years old) and when all said TV adaptations are set. It could well have been called Wodehouse Time also.

The historical name for this period is the Interbellum, hence the name. Later portrayals may see it combined with Dieselpunk.

In his short story Umney's Last Case, Stephen King refers to a temporal variant, Chandler American Time.Here, the action is set at the very end of the period, just before America enters the War in 1941.

See also Old Dark House, which is usually the setting for Ten Little Murder Victims.

Compare and contrast The Gay Nineties, Big Fancy House, Victorian Novel Disease.

Board Games

 * Clue / Cluedo

Film

 * Gosford Park
 * Our Dancing Daughters
 * Bright Young Things, the film version of Waugh's Vile Bodies
 * The Thin Man film series, depicting the adventures of Nick and Nora Charles.
 * The film version of Mrand Mrs North.

Literature

 * G. K. Chesterton's Father Brown stories.
 * Former Trope Namer Agatha Christie:
 * The Secret Adversary (1922), which introduced Tommy and Tuppence not so long after they were both out of work due to the end of World War I. Partners in Crime (1929) is a series of linked short stories about their joint venture in running a detective agency. Unlike Poirot mentioned above, Tommy and Tuppence aged roughly in real time.
 * Christie's final novel Curtain actually does provide a timeframe for her stories (or at least the ones about Poirot, though this would probably drag a lot of others into the mix as well by proxy due to overlapping characters), placing them in the period of the early 1920's through the early 1940's. This may not always be consistent with the details of all of her stories but at least it's established.
 * Kerry Greenwood's Phryne Fisher mysteries, which are mostly set in Australia during 1928 (although the last two books have moved into 1929, and Murder in Montparnasse had flashbacks to post-World War I Paris).
 * Ngaio Marsh's Roderick Alleyn mysteries.
 * The Lord Peter Wimsey Mysteries by Dorothy L. Sayers.
 * Various books by Evelyn Waugh (most notably Vile Bodies and Brideshead Revisited)
 * PG Wodehouse's Jeeves and Wooster stories are often remembered as this, but in fact they do have occasional references that establish the passing of time (there's a past-tense mention of World War II in at least one of the later ones, and so on). The TV series is definitely and deliberately set in Christie Time, though.
 * Jean Ray's Harry Dickson novels.
 * E. F. Benson's Mapp and Lucia books.
 * Leslie Charteris' first few dozen stories about The Saint. But poor old Simon Templar, an RFC veteran from WWI, was still debonairly thirtyish in WWII, and still in harness in the 1983.
 * Jo Walton's Alternate History Small Change trilogy takes place in an extended Genteel Interbellum Setting: Britain's fascist-sympathetic government stays out of WWII, while one main character is a homicide detective whose investigations drag him deeper and deeper into a conspiracy trying to keep it that way.
 * Most of H.P. Lovecraft's stories take place in this time period, appropriately enough as it covers the span of his litterary career and far preferred Ye Olde Anglo-Saxon way of life to the hustle and bustle of contemporary urban America; as the setting is Lovecraft Country, it remains credible.
 * S.S. Van Dine's erudite and sublimely supercilious Philo Vance.
 * Many of Rex Stout's early Nero Wolfe novels are set in this period.
 * Richard Lockridge's husband and wife detectives, Mrand Mrs North.
 * Dashiell Hammett's The Thin Man epitomizes the high-life in New York during this period.
 * The Phantom Detective provides a pulp-hero version of the genteel detective.
 * The Grimnoir Chronicles occurs in an alternate history where individuals capable of magic started being born the previous century. As such it has diverged in a few notable ways, such as magical fire and lightning control making zeppelins far more prominent.

Live Action TV

 * Doctor Who: Black Orchid and "The Unicorn and the Wasp", plus bits of Carnival of Monsters.
 * Downton Abbey
 * Jeeves and Wooster
 * The opening titles are practically the Genteel Interbellum Setting incarnate.
 * Poirot
 * Upstairs, Downstairs and its lookalike The Duchess Of Duke Street, for the most part, though both actually run from about 1900 to 1930.
 * Brass, a comedic British Nighttime Soap Affectionately Parodied this style of drama, as well as Dallas and the like.

Newspaper Comics

 * Rupert (which actually began in 1920) and other British children's Newspaper Comics.

Tabletop Games

 * Eberron is, by default, set in a fantasy equivalent.

Theater

 * Basically all of Noel Coward's comedies, such as
 * Blithe Spirit
 * Easy Virtue
 * Private Lives
 * Lend Me a Tenor
 * Operatic example: Lennox Berkeley's chamber opera A Dinner Engagement.

Video Games

 * Laura Bow
 * The Professor Layton series seems to be set in this, but the anachronisms flow so thick, you might as well chalk it up to Purely Aesthetic Era.
 * The Amiga game Murder! is set in this kind of environment; the player character is in a mansion with a dead body and a lot of guests with secrets and has two hours to solve the crime before the police show up.
 * The Last Express is set in 1914, just before WWI, is filled to the brim with Art Nouveau and is about a murder on the Orient Express.