Spoilers for A Haunting in VeniceKenneth Brannagh's third Agatha Christie adaption, A Haunting in Venice, is the darkest one yet, as its horror aesthetic leads to some pretty shocking and brutal deaths. When Hercule Poirot is invited to a Halloween party and séance, things turn for the worse when a dead body is discovered, and Poirot is forced out of retirement to solve the case. There are four deaths in A Haunting in Venice, three of which are murders.
https://screenrant.com/haunting-in-venice-everyone-who-dies-clues/