She started a novel with Alleyn in 1931, after reading a detective story by Agatha Christie or Dorothy L. Sayers on a wet Saturday afternoon in London and wondering if she could write something in the genre.
So she bought six exercise books and a pencil at a local stationer and started A Man Lay Dead, involving a Murder Game, which was then popular at English weekend parties.
Roderick Alleyn (pronounced 'Allen', and known as Rory to friends) is a gentleman detective, whose family and educational background may be deduced from comments in the novels.
When the series opens (A Man Lay Dead, 1934), Alleyn is aged about 40 and is already a Detective Chief-Inspector in the CID at Scotland Yard.
As the series progresses, Alleyn marries and has a son, and eventually rises to the rank of Chief Superintendent.
When he returns to England, to his wife, Agatha Troy—and to a murder case—in Final Curtain (1947), Alleyn observes that they have been apart for "three years, seven months and twenty-four days".
In Artists in Crime (1938), their mother indicates that Sir George is more conventional and less intelligent than his detective younger brother.
Troy is a famous painter, particularly of portraits, and features in many later novels either in person or in the letters Alleyn writes to her.
Alleyn was reportedly educated at Eton and Oxford, and worked in the British Foreign Service for a year (1919–1920) before joining the Metropolitan Police.
Assuming both gentlemen graduated with a typical three-year Oxbridge degree at around age 21, then in 1934 or 1935 Bathgate is about 22 or 23 and Alleyn is about 20 years older, indicating his birth was around 1893 or 1894.
The sixth novel, Artists in Crime (1938), rapidly follows the action of Vintage Murder (that is, occurs in late 1936), and contains letters between Lady Alleyn and her younger son during his return to England.
The setting of the novel is identified as being contemporary with its writing, i.e. the early 1970s, and while Alleyn is clearly a senior member of CID, he is still relatively young and fit enough to be "sprinting" down alleyways after perpetrators.
The script of a television play by Ngaio Marsh, A Knotty Problem, which features Alleyn and is set in New Zealand, appears in the anthology Bodies from the Library 3 (Collins Crime Club, 2021).
[citation needed] Four novels were adapted for New Zealand television in 1977 under the series title Ngaio Marsh Theatre, with Alleyn played by George Baker.
In the pilot, Artists in Crime (1990), Alleyn was played by Simon Williams, and then by Patrick Malahide in eight more tales (1993–94): A Man Lay Dead, The Nursing Home Murder, Final Curtain (the second TV adaptation), Death at the Bar, Death in a White Tie, Hand in Glove, Dead Water and Scales of Justice.
Four stories were recorded between 2001 and 2006; A Man Lay Dead (2001), A Surfeit of Lampreys (2001), When in Rome (2003), and Opening Night (2006) The Inspector Alleyn Mysteries (the 1990s British productions) are available on Region Two DVD as a four disc pack.