As I’ve been reading the Poirot short stories and novels, it’s struck me that it’s not just once or twice that it was the murderer who called Poirot into the case. I don’t want to go into a list, since merely to name them would consist of spoilers, but off the top of my head I can think of at least four novels and a short story in which the murderer called Poirot into the case and two more short stories about robbery rather than murder in which the thief called Poirot in. I’m confident that this is not an exhaustive list. I’m really not sure what to make of this.
If it happened merely once, it would be an interesting twist. Happening so often, it feels like something else. What, I’m not entirely sure. A few possibilities recommend themselves.
One possibility is that by frequently having the person who called Poirot in be the criminal it keeps the reader more on his toes. I’m not sure this really works, though; there’s a certain foolishness in calling in the world’s greatest detective to investigate your crime. It becomes more foolish still after reading about his cases in the newspaper (or in Captain Hastings’ records of them) and seeing how often he’s willing to accuse the person who hired him. If I murdered someone in the 1930s and I was determined to call a detective in to investigate the case, I would far rather call in Giraud than Poirot.
Another possibility is that this was merely a solution to the problem that all mystery writers face of how on earth you get your detective in on the case. It is, of course, possible to go the Jessica Fletcher route and simply have the astonishing coincidence that the detective just happens to be around murders ten to twenty times per year. Those who want a little more realism need to be more creative. The problem with calling a detective in before the crime is committed is that, in general, there is only one person who knows that the crime will be committed—the criminal. The major alternative I can think of is a person who suspects that attempts have been made before against his life calling in the detective. This works, but requires either a remarkably incompetent murderer or slow poisoning. The murderer calling in Poirot does open the field a bit.
The tradeoff is that it is mostly not in the murderer’s interest to call the world’s greatest detective in, which makes it very hard to make this plausible. Of all the times that it happened with Poirot, I’m inclined to say that the A.B.C. Murders was probably the most plausible. The murderer had a legitimate (from his perspective) reason for it to be Poirot and not someone less well known. The murderer also produced a very clever series of murders, complete with a scapegoat who believed that he did it, so it was plausible that Poirot might have been fooled, or else that he would have been overruled by the police.
As for the other times, the criminal calling in Poirot seems far less excusable. It was mostly pretty gratuitous. Granted, Poirot tries to be underestimated by criminals, but it seems odd for so many criminals to take such an unnecessary risk. Especially because it’s usually with very little gained by bringing him in.
Which leads me to suspect that it really is done merely as a way of bringing Poirot into the story. I’m hesitant to believe that’s the case, though, since Agatha Christie is such a master of plotting. Overall, I’m not sure what to make of it. All I’m sure of is that it’s strange.