The Basics Of Writing A Mystery Plot

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First, let's look at what makes a mystery plot.

Mystery plots might seem like complicated things at first, but they're actually quite simple! It all starts with a scenario that presents a big question (EG, "who did this?"). Then someone follows a trail of clues to find the answer. It's not unlike a treasure hunt game, where you're given a piece of paper that gives you a hint to where the next piece of paper is, which gives you a hint to the next one - and so on and so forth until you finally reach the treasure. Just as a paper that says "let sleeping dogs lie" might tell you that you should probably look for the next paper in Rover's bed, a bloodied store uniform shirt near a murder scene might tell an investigator that the perpetrator might be an employee of the store, and so that's where to start looking to start forming a pool of suspects.

So what you have to do is this: figure out the truth that your investigator will ultimately discover (EG, what exactly went down to create the scenario the investigator comes upon, such as the dead body or the ransacked room). Figure out exactly who did it, how, and why, and then work out a trail of clues that could lead your investigator to this discovery. (This is not to say that there must only be one potential trail to follow - realistically, there could be many potential paths - but ultimately, you must commit to one path for your investigator to take.) It works best if you work backwards as well as forwards, and look at it from the perspective of the perp to figure out what the perp might have done (or not done!) that could leave a trail (or a few trails) the investigator could follow.

The audience needs to learn and think alongside the investigator.

There are two big reasons people get into mysteries. One is so they can vicariously experience solving the mysteries through the investigators, and the other reason is so they can try to puzzle out and figure out the solutions themselves as they go along.

First, you need to show your investigator finding the clues - and every clue. You can't just have your investigator up and announce some important fact or detail that the audience had no way to know about, or else the audience is going to feel cheated.

Secondly, you can't have your investigator come to an unexplained conclusion. For example, you can't have your investigator just look at a murder scene and then trot off to some nightclub with absolutely no explanation. Instead, you need to have the character explain (to a partner, perhaps) or mull over what it is about the murder scene that makes the the nightclub seem like the next place to look.

So whatever your investigator learns or concludes, make sure the audience is in on it, too. Otherwise, you undermine the reasons people came to your story in the first place!

Make sure you don't accidentally have your investigator jump to unfounded conclusions.

One common rookie mistake in mystery fiction is to have the investigator come to a conclusion that isn't actually as well-supported by the evidence as the author assumes. As the writer, it's easy for you to see why the evidence leads to a particular conclusion, but you have to remember that for your character, it should be a whole different story.

One thing you must remember is the principle of equifinality. Basically, any end state your character might encounter can be reached more than one way - which may or may not actually have anything to do with the mystery. Maybe that scrap of cloth in the woods was left by a fleeing suspect, or maybe it was left by someone who suddenly remembered that the stove was still on at home. Someone with a shirt covered in cat hair might be a cat owner, but this person might also be a pet sitter or shelter volunteer, or the person might have snuggled a cat belonging to a neighbor. A droplet of blood on the floor might mean that something violent happened here, or it might just be that someone had an accident and walked this way before getting it cleaned and bandaged. Any competent investigator will be aware of possibilities like these and will take them into consideration, waiting to see what the rest of the findings point to before drawing any firm conclusions.

Another thing you should do is make sure your investigator has good reasons for believing that anything particularly out of the ordinary is going on. For example, if an elderly senator with a history of bad health and an unhealthy lifestyle dies of a heart attack, your investigator needs more than a funny gut feeling to realize that this senator was in fact assassinated - there needs to be something somewhere that actually points to an assassination. One thing you might do is ask yourself what a case where an elderly senator passed away from perfectly natural causes would look like, then ask yourself what makes this case any different from it. If you can't come up with an answer, your investigator is jumping to unfounded conclusions and others are well within their rights to doubt this character - even if it turns out that your investigator was right the whole time. (Even a broken clock is right twice a day!)

It all needs to make sense in hindsight.

Whatever the truth behind the mystery turns out to be, the facts and details surrounding the case need to be congruent with it when you stop and think it through. It doesn't work to have your investigator find a trail of bicycle horns and red rubber noses only for the perp to turn out to be someone with no reason to keep, carry, or leave behind clown accoutrements. You can't have your perp break into a high security area with expensive tools and professional skill, only to turn out to be an average high school student with no connection to anyone who could have provided the necessary training or tech, nor provided the money to get it. Nor can you have your investigator see a pale, translucent figure levitate and walk through solid walls only to have it turn out to be a regular guy wearing a sheet - because unless your investigator was on some mind-altering substance or something, a ghost is still a more plausible explanation. So stop and ask yourself: Just how did the perp accomplish everything that the investigator sees and/or finds out about? And why did the perp do it that way?

The same principle goes for misdirection and false leads - they only work when they take advantage of plausible equifinality. For example, it works to reveal that your investigator was chasing down the wrong person because the real perp wore someone else's coat on the night of the crime to avoid recognition. It doesn't work to reveal that the real perp is someone who was mingling with other people around the time the crime happened and realistically never left their company long enough to commit the crime in question. Whatever the truth is, it needs to be at least as plausible as the wrong conclusions your investigator makes.

In summary!

• At its core, the structure of a mystery plot is simple enough - something happens at the beginning of your plot that poses a big question, and your investigator follows a series of clues that leads up to the answer.
• Your audience should always be able to see your investigator discovering the clues that lead up to solving the mystery, and be let in on the investigator's line of reasoning that leads up to any particular conclusion.
• Remember the principle of equifinality - that any particular end state can be reached more than one way. A spot of blood on the floor might be from a violent incident - or just from a household accident. A competent investigator will take this into account!
• Remember that extraordinary conclusions need to have extraordinary evidence. If your character believes that someone was assassinated rather than died of natural causes, there better be something that sets this death apart from an actual natural death.
• The facts and details surrounding the mystery need to make sense once we learn the truth. It doesn't do to have it so that your perp did something that would actually be impossible if you thought about it, or just made no sense to do.
• If you use misdirection or false leads, the reality of the matter must be equally as plausible. It doesn't work to have the "real" story make little to no sense when you think about it.