Murder In Retrospect
Murder In Three Acts
Hercule Poirot is a love-him-or-hate-him kind of detective. Unlike Sherlock Holmes (or CSI), he is not big on physical evidence. He instead solves mysteries by speaking with the people involved, and solving crimes almost by psychology. It is probably inevitable that such a detective would appear in the wake of the explosion of psychology and popular theories of the human mind in the first half of the twentieth century; it is to Agatha Christie's credit that Poirot's methods are far subtler than a trendy follower of psychology would make them. If a man kills his employer, it is because that employer made his life hellish for years, not because he was revolting against an authority figure, or because of the collective unconcious, or things like that.
The only real flaw of these novels— and you may not consider that it is a flaw— is that Poirot's reasoning is held close in his head until the final exposition. There's little chance for a reader to figure things out except by lucky guess and by the dictum that the obvious person is never the actual killer.
(They're like popcorn! You just keep munching...)