A murder mystery or detective story where the location of a crime plays a central role. Also: where-dunit.
In some mystery novels, the wheredunit is as important as the whodunit. The locale, rather than merely serving as the backdrop to the plot, is an essential ingredient that lifts the story out of the ordinary, providing an ambience found nowhere else.
—Robert Wade, "Blood flows in the wilderness as fast as it flows in the city," The San Diego Union-Tribune, September 19, 2004
At the police station, Young-min readily and surprisingly owns up to his gruesome crimes, and Jung-ho sets out to find Mi-jin. "The Chaser" is less whodunit than wheredunit, perversely withholding the location of Young-min's home from everyone but the viewer, who gets to know Seoul's Mangwon district quite intimately as Jung-ho, his bumbling sidekick Meathead (Koo Bon-woong) and other cops run around it in infuriating circles.
—Justin Chang, "The Chaser," Daily Variety, June 9, 2008
"California Street" is an innovative variation on the detective-novel formula, sort of a psychological whydunit in addition to a whodunit. Interestingly enough, such variations are getting to be the rule rather than the exception. From Conan Doyle's Sherlock Holmes tales to Robert Parker, mysteries have had a large element of the howdunit. But lately, the other interrogatives have dominated. Taking us to Japan or New Mexico, mystery writers such as James Melville (the Inspector Otani series) and Tony Hillerman have pioneered the wheredunit. With settings as disparate as 12th-Century monasteries and 1940s L.A. jazz joints, writers such as Ellis Peters and Walter Mosley take us on whendunit time trips to solve crimes. (I suppose you could also argue that Stephen King and Clive Barker often are writing whatdunits.)
—Digby Diehl, "Psyching out a killer," Los Angeles Times, November 11, 1990
This genre-twisting term is of course a play on the venerable whodunit, a generic and colloquial reference to any murder mystery or detective story. (Ask the Oxford English Dictionary for the etymology of whodunit, and you get this delightfully snobbish response: "[repr. who done (= illiterate for did) it?]".)
The earliest citation is a terrific piece of writing that manages, in just a few sentences, to take the classic interrogative pronouns — who, what, where, when, and why, also known as the "5 W's" — and blend each of them with the suffix -dunit to nicely summarize the murder mystery genre. However, although that 1990 cite is the earliest for wheredunit, the others are all much older: whodunit goes back to 1930; whatdunit dates to 1948; whendunit first appeared around 1957; and whydunit showed up around 1947.