This is the second story to feature Ariadne Oliver, played by Zoe Wanamaker.
Christie's book "Mrs. McGinty's Dead" was the source for Murder Most Foul (1964), with a very different plot and with Miss Marple as the sleuth, not Poirot.
This episode appears to be the first one shot on 24 frame video, due to some tell-tale image artifacts.
Mrs. Oliver drives a 1936 MG TA.