OK, this book is CREEPY; not so much for the story, but for the identity of the murderer!
Story is set in a "crooked" little house called Three Gables, where lives a wealthy old man along with the rest of the tight-knit family, including a young, beautiful wife. He dies of poisoning under mysterious circumstances and everybody jumps to the conclusion that it must be the wife, and her assumed lover, who did him in. But did they? For, the entire family feels that these two might not have done it. But then, that'll mean one of their own blood is the culprit; so they all hope against hope, that the "right person" murdered the old man.
This novel isn't a part of any series, so no Poirot or Miss Marple or Tommy and Tuppence in here, but it's compelling just the same. As always, the murderer is absolutely the LAST person you ever suspected; even more so in this case! Christie proves, flawlessly, yet again, that it takes all sorts to make a world.