Plot holes, inconsistencies, odd behavior etc. *spoilers*
Maybe it is just me, but do the ongoings in the movie make any sense to anyone?
- Why would the doctor drop his dead wife in precisely the house which he hopes to win eventually by her death? She and her marital problems have no direct connection to that house, and he is artificially underlining the connection by putting her there.
- Why kill her in a train? That is most risky. Anyone might pass by on the aisle anytime. People in the neighboring compartments might hear something.
-Can you even open a train window that wide that you can throw a body through it?
- Why would he put her in a sarcophagus, inside the garden? She would start to smell eventually, it is impossible that no one would notice her. How is it even possible that the dog does not react to her presence? There is ample empty space outside the garden, why not simply bury her there where he would not be in danger to be observed by the gardener or the boy? Why not kill her anywhere else in the first place?
- Why did the boy leave such a chaos when he searched her room to steal the device?
- How come that the family does not react emotionally in any way to the death of two brothers? Their behavior does not change even the slightest bit after their death. It is like nothing happened. No fear, no joy, no grief. They do not even reminisce about the dead.
- Why did the doctor to kill other people that hastily? Obviously such a killing spree has to attract quite some attention by the police and the public, while reducing the number of suspects for the first murder at the same time. Poisoning could be done in a much more discrete way.
- How did Miss Marple ever conclude that the dead woman was the doctor's wife? There are plenty other possible explanations for the ongoings, even if you decide that the doctor is the murderer; how the heck did she guess the right one? For the reasons stated above, this one does not even make much sense.
- How can the doctor possibly hope to get away with just another murder (Miss Marple) by simply explaining it away as a heart attack? Another dead in that house has to provoke a most exhaustive investigation, and in that last case he would be the most natural suspect. In particular as Miss Marple mentions explicitly that the boy knows that the doctor is visiting her. He would have to admit right away that she died in his presence.