If you’ve ever felt let down by the end of a mystery novel, there’s a good reason why. The biggest secret in crime fiction is that there are really only, like, four ways to tie up a mystery, and I’m going to show you all of them in 1,200 words. Get ready to have an entire genre irrevocably spoiled.

1. The Obvious Killer

“I know it was you, Ignatius Didit. I knew it when you shook my hand, and I saw something dark crusted under your fingernails. I knew it when I heard peculiar noises coming from your basement and decided not to investigate them for some contrived reason. I knew it when your alibi fell apart. I knew it by process of elimination, because everybody else who might have done it is dead. But, really, I knew it the first time I met you; when I visited you at your place of business, I saw that the sign above the door said: ‘I. Didit, Purveyor of Fine Hatchets, Cleavers, and Shovels.’ Your guilt couldn’t be more obvious. The only reason I thought it might not be you for a while is because it seemed too manifestly self-evident. But it’s apparently you. So, I’ve got to say, I’m pretty disappointed.”

2. The Tertiary Perpetrator:

A. The Forgettable Man

“Who is that? Oh, it’s you. Yes, I recognized you. It just took me a second, because I haven’t seen you for, like, 200 pages. And, to be honest, you didn’t really make much of an impression when we met. Honestly, I probably wouldn’t have remembered you, except that somebody very pointedly and deliberately reminded me about you two chapters ago. I should have expected that you’d be showing up again. Otherwise, why would anyone even bother to mention you? What are you doing here? And why have you got that knife?”

B. A Little Too Friendly

“I swear, sometimes this detective job gets to me; drives me to the bottle. You want a swig? No? More for me then. Everybody’s so awful. I know most of them are innocent, at least of the murder, but they’re all so cagey. Everyone here seems to have some dark secret, and they’re so fast to lie or conceal things from me. It just shatters my faith in mankind. They’re so hopeless. All of them except you. You’ve really been a friend to me, these past few days. You’ve been so happy to divulge everything you know and to tell me all about the reclusive oddballs who live in this Norwegian fishing hamlet where the sun only rises for three hours a day. You’ve helped me keep track of the byzantine genealogies of the feuding local families, and you’ve offered your extensive local knowledge in service of my attempts to identify inconsistencies in their stories. I wouldn’t be anywhere without you, and I hope we will remain close friends when this is all over. Why are you laughing so sinisterly?”

C. He Mostly Kept To Himself

“Pardon me, I was just passing by on my way to accuse somebody else of being the brutal serial murderer who has terrorized this neighborhood for the past few months, and I happened to notice an odd stench coming from your apartment. Is everything okay in there? Do you mind if I have a look around? It seems like — OH GOD! OH GOD! OH GOD!”

D. Here Comes A New Challenger

“Who are you? Oh. You’re the victim’s ex-fiance. Isn’t it odd that I’ve been investigating the murder for the entire book, and we are just meeting now, for the first time, on page 320? I think someone told me about you, but I didn’t think much about it at the time. What? You say you eloped with her, and you were secretly married? I guess that explains the receipt for a plane ticket to Las Vegas that I found in her desk. But if you’re her husband, and the whole family is dead, then that means you’re the sole heir to the largest combination yarn store and kitten shelter in all of New Hampshire! That’s your motive, you conniving rapscallion! And you would have got away with it, too, if it weren’t for me, the Etsy detective and my associate, Mr. Mittens, the wiliest tomcat in New England!”

3. The Master Of Deduction Goes To Work

“Watson, you’ll notice from these footprints that the perpetrator wears one shoe in a size nine and-a-half, and another in a size 11.”

“That seems most convenient, Holmes.”

“Yes, I find things usually are. Now, if you examine the footprint more closely, what else do you see?”

“It looks to be the tread of a work-boot.”

“Perhaps I don’t tell you enough that you’re stupid, Watson. I mean, really, you have a special gift for pointing out the obvious. How did you become a surgeon anyway? What happens when you operate on someone? Do you saw open the poor man’s torso, and then notice that his chest seems to be full of organs?”

“What do you see, Holmes?”

“You can see that the boot print contains some red dirt. That’s brick dust. This is very fortuitous, because each clay-bed has dust of a unique color, so I can always tell where someone has come from, as long as they’ve wandered through a brickyard. And criminals are always wandering through brickyards, I guess.”

“That also seems awfully convenient.”

“It’s like I always say, Watson: When you eliminate all the inconvenient possibilities, what remains, however implausible, might as well be the truth.”

“Quite right.”

“Now, over here, we have a bit of pipe-ash. The leaf from every tobacco store in London is unique for some reason, and therefore identifiable by its ash. I can triangulate the area between the pipe-store where this tobacco came from and the brickyard where the dust came from, and then we have only a three block radius in which to look for the man with the mismatched feet!”

“Extraordinary!”

“And wait! What’s this? Why, it’s the pollen of the African violet, which I can identify on sight even though it’s practically microscopic and looks pretty much the same as any other pollen. There is only one window box in that neighborhood that contains African violets. By the way, I evidently know the location of every single weed or blade of grass in all of London. We have narrowed our search to but a single building, and now I know the name of the man we’re looking for!”

“How is that possible?”

“I don’t mean to be mysterious, my dear stupid Watson. I shall tell you everything, just as soon as I snort up all this cocaine.”

4. The Big Twist

“Look! It is I! You thought I was dead, but I am not dead. I am still alive, and I tricked you. Also, I am not really a woman; I’m actually a man. I’m the brother of the boy who was hit by the train 20 years ago. I never disappeared. I’ve been here all along, in disguise. Also, are you ready to have your mind blown? You and I are actually the same person. That’s right. We’ve been the same person all along. If you think about it, it totally makes sense. Also, this isn’t really New York City. It’s actually purgatory. But it’s not really purgatory; it’s more like a computer simulation of purgatory. And the computer is a ghost, but it doesn’t know its dead.”

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