Luke Obiako Fitzwilliam's character is based on the 1939 book's Luke Fitzwilliam -- a role that has been played by Bill Bixby in the 1982 TV movie, Peter Capaldi in the 1993 London stage version, and Benedict Cumberbatch in the 2009 TV version alongside an additional amateur detective, Julia McKenzie's Miss Marple.
The winner of the Epsom Derby in 1954, when this adaptation of Murder Is Easy is set, was Never Say Die, ridden by Lester Piggott. Miss Pinkerton's horse, Jujube II, is fictitious, taken from Agatha Christie's original 1939 novel and named after a Chinese fruit that is also grown in Africa.
Douglas Henshall (playing Major Horton) and Mark Bonnar (playing Rev. Humbleby) appeared together for 7 seasons as key characters in the crime drama Shetland
Tom Riley (Lord Whitfield) previously appeared in episodes of Miss Marple and Poirot