I like Agatha Christie novels a lot, and one reason is that the end is often deducible. In Sherlock Holmes stories, they usually pull something out at the end that you’ve never heard of, but in Agatha Christie you’ve met the murderer and understood the motive by the end of the first act. However … I just saw a Miss Marple mystery on Netflix in which … well, I think it’s best explained by a short one-act play which shows how I imagine the co-conspirators came up with their plan.
[SPOILER ALERT]
A: Hey, I think we should kill my cousin for the inheritance money and I’ve got a great way to do it.
B: Great! What did you have in mind?
A: All right, here’s what we do. First, we find a girl scout that kinda looks like my cousin. We tell her we’re film executives and ask her to come by the hotel the night we’ll murder my cousin. We bring her in, do her hair, put her in my cousin’s dress, and drug her. Next, you drive her to that playboy’s house, strangle her there and leave the body.
B: Wait, I thought we were killing your cousin?
A: I’m getting there. See, all this time, my cousin has been dancing in plain view of everyone on the ballroom floor. When you get back from the playboy’s house, we drug her too and tell her to go to my room. She’ll fall asleep, at which point we kill her. We can be playing bridge in front of everyone for almost this whole time, which can be our alibi. The next day, we’ll dress my cousin in the girl scout’s clothes, steal someone’s car, drive her to the abandoned quarry and light the car on fire. See, everyone will think the girl scout is my cousin and vice versa!
B: Doesn’t the playboy know your cousin? Won’t he know it’s not her?
A: Oh, he’s a drunk. I’ll go identify the body at the morgue and the police probably won’t let anyone else see the body, right?
B: Um, okay. So, that’s one plan. But also — hear me out — since we’re going to drug your cousin anyway, why don’t we just put cyanide in her drink instead of sleeping pills? She will drop dead on the dance floor and no one will be able to trace it back to us.
A:
B:
A: That’s stupid.
B: You’re right, that’s stupid. Don’t know what I was thinking.
A: Shall we go find a girl scout, then?
B: I’ll drive.