One of the great things about Agatha Christie is that liked to use plot formats as a challenge to keep things interesting for herself. She wrote novels almost the way great short story writers would write short stories, each an experiment in concept or story-telling. She did this not only with standalone books like Ten Little Indians, but also in her series work.
Some of these little experiments are real gems, though many are forgotten. I only recently stumbled across the Poirot tale, The Five Little Pigs. I think this story deserves to be better known, but I suppose the charm of the story is more intellectual than most.
It's the story of a cold case. Sixteen years earlier, a woman was convicted of murdering her husband. She herself died in prison soon after the conviction. Now her daughter, who had been a tiny child at the time of the murder, comes to Poirot and asks him to look into the case.
The subsequent story is almost like a dossier. Poirot interviews all the investigators and lawyers, then the five principle witnesses of the case (the "five little pigs"), and then has each of those five principles write a first person account of the murder. Then he visits them each again with a follow up question.
The interesting thing about this story is that what we get is the same story told over and over again 15 times, by 10 different people. And each time, we see deeper into the story, and the lives of the characters. And each of the witnesses, separately, give us a view of the others; how they were then, how they are now.
So it starts as a plain puzzle story, intriguing intellectually but cold emotionally, but by the end, you drawn into the lives of these characters, caring at last for them all, wishing that this would be like Groundhog Day and that the end of the story could change if only the characters could learn from the revelation.
Perhaps that description makes the story sound better than it is, though. Certainly this isn't high literature. And the characters, as with most Christie, are stylized. But I think her sharp psychological insight into motivation and evil is at its prime here, and she has a lot of fun using them as red herrings too. I certainly came to care about even the most disagreeable of the characters, which is, imho, a feat.
See you in the funny papers.