The source Agatha Christie novel was one of her favorites of the ones she had written along with "Crooked House" (1949).
Agatha Christie's daughter, who had approval of the script, was initially concerned that Michael Elphick's police inspector, modeled to some extent after a harder-nosed American-style police officer, would prove unpopular among the local constabulary in Devon, where she lived.
Faye Dunaway's performance is seen entirely in flashback sequences and is also completely in black-and-white because all the flashbacks are in b&w. One of the film's main posters featuring thumbnail photos of the cast has Dunaway's picture, like the others, in color.
The scene with Christopher Plummer shooting a rabbit in the woods was filmed in New Jersey and not Devon, where the rest of the film was shot. This was a scene added after principal photography had been completed--and Plummer could not return to work in England for tax reasons.