Like Murder at the Gallop (1963), this movie was adapted from a Poirot novel, not a Miss Marple novel.
This was the penultimate production in the series of four films with Margaret Rutherford as Miss Jane Marple. The last is Murder Ahoy (1964) (made the same year as Murder Most Foul (1964)), in which Inspector Craddock has been promoted to the rank Chief Inspector. After the series concluded Rutherford and her husband Stringer Davis reprised their roles of Miss Marple and Mr Stringer only once more, for a brief cameo appearance in The Alphabet Murders (1965).
While inspecting the contents of the victims' suitcase, Miss Marple finds flyers for a theatrical production of Agatha Christie's "Murder She Said", which also is the first movie in which Rutherford appeared as Miss Marple.
The music playing at the opening of the hospital scene is a reference to the television show "Dr. Kildare" (1961), down to the shot of the doors to the ward. The score alludes to the theme music from the series, "Three Stars Will Shine Tonight", composed by Jerry Goldsmith.
Miss Marple's audition piece for the Cosgood Players is a dramatic rendering of "The Shooting of Dan McGrew" by Robert W. Service.
Cosgood hopes for a play-run longer than "The Mousetrap" - Agatha Christie's famous stage-play, which has been in continuous performance since 1952, the same year that source novel "Mrs McGinty's Dead" was first published.