I’ve talked about this before, here and elsewhere, and never really laid it out. I decided it would be useful to have it here as a reference, so here goes.

There are many variants on murder mystery plot structures, many of them super-effective both as mysteries and as carrier plots for larger ideas. The five-act structure is one of my favorites for long mysteries, but P.D. James has a particularly good four-act structure (which I call the “Two Body Plot”) from which she has rarely varied much over the last few decades, and it really works very well. She has successfully used these plots as a canvas on which to paint her thoughts on class, medicine, aging, religion, and all aspects of human life and death. It’s simple and it works, and if you’re thinking of writing a murder mystery but don’t know how, it’s a great place to start.

The four-act structure is useful in general because it lends itself to relatively tight plotting, even for those of us for whom long-form plotting is not a strong point: there are three tentpole events that are always in sight, and it’s hard to get too far from any of them. (I am currently using a variant of it in THE WRONG CLIENT) The Two Body Plot variant on the four-act structure is easiest to identify because of the appearance at a predictable point of a second corpse. James of course used this repeatedly to great effect. Rex Stout used a version of this a lot (my favorite was PRISONER’S BASE), and I’ve seen it in novels by Agatha Christie and others as well.

I don’t really have names for the various acts in the Two Body Plot. I’ve seen names for three-act and five-act structures, but I haven’t really seen any I like for four-act structures. For one thing, some of the most successful TBPs are P.D. James’s, and they don’t match up all that well to the terminologies I’ve seen, partly because they don’t tend to either open or close with a bang. Rex Stout, in stories that seem to me to follow this structure uses character interactions to substitute for an inciting incident, and then a super-short fourth act. I’m going to go into the James version of the TBP, because it’s the one I most often want to refer to.

I’ve been talking about acts, but the important pieces are actually three events that I referred to as tentpoles above:

• First Corpse
• Second Corpse
• Reveal (In a James novel, the Third Corpse. No, it’s not the Three Body Plot. Bear with me.)

Each event is discrete, and usually embodied in a single scene — if it’s not “onstage”, or directly described (the first two often aren’t) then the discovery of the fact takes its place. The characters are jerked around, have visceral reactions, and usually require a scene or two to regain their bearings.

These events determine what comes before and after. In some ways, it’s scene-sequel writ large. One of the ways that these plots differ from others is the sense of anticipation: first of the First Corpse (because we know that this is going to be a murder mystery and so someone’s going to die) and then of the Reveal — everything after First Corpse is moving toward that. The reader knows it has to be there, and expects it.

The events occur at the Act boundaries and while they dominate the impact of the story, they are generally only a small portion of the text. So let’s go through the Acts.

Act 1: This is a setting of the stage, and has multiple functions: introducing the main players and the setting and building some tension. In a James novel this is usually a series of character sketches and conflicts in which the victim-to-be plays a major role. (In her novels, it’s often pretty easy to identify the victim halfway through Act 1) Her detectives may or may not make an appearance. The murderer should at least be mentioned. In a Stout novel that follows the TBP, this is usually a different case entirely — a theft, maybe, or blackmail. The reader gets lots of information about the crime-to-be but doesn’t have a basis yet for fitting anything in.

This is where the mystery writer CAN get a pass that other genre writers don’t: anticipation of the First Corpse gives the story inherent tension that must be built in other stories. A James or Christie or Parker reader knows they’ve been promised a corpse and can enjoy they ride until then. If you’re writing in multiple genres, you don’t get that pass because not all of your readers know what to expect. But even if you do get the pass, that doesn’t mean you have to use it. Stout’s books still frequently frequently kicked off with some Goodwin/Wolfe/Cramer personality conflict to catch the reader’s interest (and also distract them from the presentation of clues).

First Corpse: As expected, someone turns up dead and sets an investigation in motion. They may have been dead for some time, or they may have been preceded in death by another victim, but this is the discovery and the focus.

Act 2: The investigation of the murder gets underway. The story unfolds according to the logic of the investigation, centering primarily on the detectives, and the characters who appeared in Act 1 are seen in a new light. The reader has seen them before, even if the detective hasn’t, and watches for changes. The suspects are often formally (re)introduced, even though we’ve met them all already; this way the introductions actually stick — a neat trick that Patrick O’Brian uses too.

This part of the story is primarily reactive. Procedures are followed more than insight. The detective is identifying the hurdles that need to be crossed, but not actually crossing very many of them. Witnesses hold things back, and the reader generally knows it. The reader is more generous with fumbling at this stage. Sometimes the detective is right on the verge of a major discovery at the end of the second act, but…

Second Corpse: Someone else turns up dead, very often a prime suspect. It is this body that makes the plot a Two Body Plot, not just because of cardinality but because it represents a major failure. The detective has been slow and the villain quick. Often the second corpse had critical information that the detective failed to ask for in time, or which they failed to provide for some reason (they didn’t think it important, they wanted to exert some control over the villain, etc). The second corpse may have predeceased the first corpse, but being found second they play a different role in the story.

Act 3: This is the main part of the investigation, in which the detective starts driving the investigation through insight rather than procedure. They’re reeling after the second corpse, and probably rethinking a lot of things, but all the villain did was buy themselves time. The detective is regaining control, and the villain is in reaction mode.

In a TBP, the same person usually is responsible for both corpses; often some paragraph or two is spent explaining why this has to be the case, but sometimes the Two Murderer Theory is explored. But the reader is less patient with the detective at this stage (some readers will have guessed the solution!) and any blind alleys followed need to pay off sooner rather than later. Events are set in motion by both the killer and the detective, and the detective’s success (or trickery) raise the pressure on the off-stage villain. The detective forms and discards theories, but at the end of the third act must know the identity of the killer but typically not how to prove it. This paves the way for the…

Reveal (or Third Corpse): The detective and the killer finally, briefly, clash. In a James novel, very often the killer strikes again, and the reader has a moment of believing they’ve succeeded (hence “Third Corpse”), but they’re thwarted by the detective at the last minute — sometimes the detective is the intended third corpse, but usually not. In a Stout TBP novel, this is usually a trick played by Wolfe (often with Archie in the dark, and always with the reader in the dark) and nearly always a confrontation including multiple people and often the police.

A word about the reveal: it has been said, and I agree, that the optimal time for the reader to guess the identity of the killer is three paragraphs to a page ahead of the detective announcing the solution. Just enough time for the reader to be excited and proud of themselves, and not enough time to get bored waiting for the detective to catch up. That means that while the scene in which the reveal takes place might luxuriate in description or a gloating retelling of events, the reveal itself often needs to be expressed in a very short length of text.

Act 4: Although I called the previous event “the reveal”, it often is parsimonious in its explanations, keeping strictly to the identity of the killer and other sources of immediate tension. People may still have done suspicious things, and the detective may have acted mysteriously — these explanations come in Act 4. The characters we met in Act 1 get on with their lives. This is often a short act, but an important one in a James novel, where we’ve spent a great deal of time getting invested in the personal lives of some of the suspects. If this is part of a series, then there’s usually some long-term arc progression or wrap-up going on here, too (Dalgliesh’s romance and eventual marriage, for example).

…

And that’s it! It’s very simple, but you see it over and over because it’s such a useful starting point when planning a new murder mystery. (As James D. Macdonald says, “The oldest engines carry the heaviest freight.”) There’s a lot to play around with there, and filling in details about those seven parts will help you get at what you want out of your mystery.

If you’re still stuck, and this structure appeals to you as a starting point, I suggest focusing on First Corpse and Reveal first. Those are the two parts that get at the heart of the two relationships at the very heart of the story: The villain and the victim, and the villain and the detective. For the first relationship: Is the killing a vicious one? A desperate one? Is it clearing away the obstinate old order, or is Saturn devouring his children? For the second relationship: is this coming down to a physical confrontation? An elaborate trap? An elaborate trap that goes wrong? Is the villain tricked into confessing, or are they caught in the act of trying to silence that last witness?

Once you’ve got answers that make you happy (for now), think about how those will play out and what those decisions say about the characters involved. Other aspects and characters will flow from that. All through this process, keep a word processor window or a notebook open with the main parts and acts written on it, and jot notes as they occur to you. You may start thinking in terms of prerequisites: before this can happen, the stage must be arranged thusly, and I need a character in this position… It’s a bit like playing chess backward. Or you may start thinking in terms of themes and how variations on them can play out.

And of course, this is all a starting point: you’ll probably start itching to make changes to that structure as your story takes shape, and so you should. But if you don’t, and your first draft or final draft ends up exactly as above, don’t worry too much about it. Just: Tell a good story. Devise a good mystery. Start on your next one.

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If you enjoyed this article, please consider reading my novella The Liar (available in print and ebook from Amazon and other booksellers). It’s a rural fantasy with a mystery at its heart, structured in five acts. If you want to see how five-act mysteries can work, I dare say it’s not a bad example. It was a finalist for the Nebula award last year, and rather a fun piece if I do say so myself.