And Then There Were 43: Hercule Poirot's Christmas by Agatha Christie

It is in no way beginning to look a lot like Christmas, either in
the real world or inside the pages of this novel. What it *is*
looking a lot like is that rare creature, an honest-to-goodness
Agatha Christie locked room mystery! Leave your crackers and crowns
at home, but perhaps bring along a sponge or paper towel to help
absorb the oodles of blood we encounter in one of Christie's more
gruesome murder tableaux. Who would have thought the old man to
have had so much blood in him...?