4:50 From Paddington Station was also the first Agatha Christie Miss Marple story to be adapted for Margaret Rutherford in Murder She Said. Comparing the two is six of one, half a dozen of the other.
For the big screen the characters of the woman who saw the strangling on a passing train and the woman who Miss Marple sends in as a housekeeper to scout out the terrain are eliminated. Rutherford's character serves as both and one of the biggest strengths of the film is Rutherford doing her own scouting and sleuthing and her scenes with ailing family patriarch James Robertson Justice are a hoot and a half.
Joan Hickson's Jane Marple is a milder sort, but still a woman who doesn't miss much. This version is faithful to the Christie story and has a friend of Miss Marple see the strangling of a woman and her being thrown out the window of a train going the other way. But no body turns up near the tracks. At that point Hickson goes into action and determines that the body was most likely thrown off near the Crackenthorpe estate. At that point she sends in Jill Meager as an operative so to speak.
The Crackenthorpes are wealthy British family, new money, they got rich manufacturing breakfast cereal. And they've got an ailing patriarch with one of those crazy wills that provide a host of relatives as suspects.
I will say this, the same perpetrator in the Margaret Rutherford movie does the deed again in 4:50 From Paddington Station. And nearly gets away with it, but for an unexpected witness.
A little slow, but more is explained and the murder itself doesn't seem quite as contrived as the Rutherford film.