The spy novel referenced is "N or M?" which was published in 1941. After publication, she was investigated by MI5 because the character Major Bletchley shared a name with the code-breaking center Bletchley Park. When asked about the name, she replied "Bletchley? My dear, I was stuck there on my way by train from Oxford to London and took revenge by giving the name to one of my least lovable characters."
The manuscript in the film is a reference to the novel "Curtain." Written in the early 1940s, Christie insured that there would be an ending to the Poirot series, even if she did not survive the war. It was published in 1975 and was the last of her novels to be published during her lifetime. The final Miss Marple story, Sleeping Murder, was published posthumously.
In this TV-movie, Christie attempts to sell a manuscript to avoid taxes. In reality, she admitted to slowing her output to one book a year, and would sometimes gift the royalties of her works to family members. For tax reasons she set up a private company in 1955, Agatha Christie Limited. Additionally, references to high taxes are often found in her post-war novels.
Although Agatha Christie is played by a different actress in each entry to the series, Blake Harrison returns as the fictional character Travis Pickford who was first introduced in Agatha and the Truth of Murder (2018).
Helen Baxendale (Agatha Christie) previously appeared in two Christie story adaptations: A Pocket Full of Rye (2008) and Curtain: Poirot's Last Case (2013).