(n.) a detective story in which the culprit is revealed at the beginning, with the plot following a detective’s attempt to solve the crime
The opposite of a ‘whodunnit’ is a howcatchem—a tale in which the perpetrator of a crime is revealed at the start, and the story then follows a detective’s attempt to catch them.
Admittedly, the more usual term for this kind of storytelling is simply an ‘inverted’ detective story. That makes howcatchem unsurprisingly a fairly flippant term, you’ll not find in any major dictionaries (at least, not yet). But that’s not to say it doesn’t have a well-established and somewhat illustrious history behind it.
The term howcatchem is credited to the British crime writer and screenwriter Philip MacDonald. Born in London in 1900, MacDonald relocated to Hollywood after the First World War and there established himself as one of the most successful thriller and mystery writers of the day, thanks to bestsellers like The Rasp (1924), The White Crow (1928), and The Noose (1930)—many of which featured his quintessential gentleman detective, Anthony Gethryn.
In 1931, MacDonald cemented his reputation with a groundbreaking thriller called Murder Gone Mad, often cited by detective story fanatics as the very first work of crime fiction featuring a serial killer. The jury’s still out as to whether that particular fact holds true or not, but Murder Gone Mad did break the mould in at least one respect: it is credited with being the first major work of crime literature to feature an entirely motiveless antagonist—a mass murderer, spurred on purely by blood lust, known as The Butcher.
The way MacDonald’s story unfolded meant that the reader was introduced to The Butcher and his homicidal ways at the opening of the novel, after which the action was switched to Scotland Yard’s attempts to track him down. This inversion of the usual crime novel format led MacDonald to later describe Murder Gone Mad not as a traditional whodunnit, but as a “howcatchem”:
The stories themselves, as examples of ... different types of what is now (unfortunately, I think) generically labeled “Mystery Story,” seemed to me to hold up pretty well: The Rasp as a pure, dyed-in-the-wool Whodunit; Murder Gone Mad as a tale of mass-murder, half Whodunit and half (to use a label of my own coining) Howcatchem.
Three for Midnight, Philip MacDonald (1963)
From there, howcatchem fell into broader use in the 1970s—largely among pop culture critics and writers looking for a suitable term to describe the similarly format-inverting stories like those played out in Columbo. The immense success and longstanding popularity of Peter Falk’s shambling genius, LAPD detective Lieutenant Frank Columbo, has since established this series as the true benchmark of this kind of inverted writing.