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 is the second story to feature Ariadne Oliver, played by Zoe Wanamaker.
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.