Clues, we all know about clues — any good mystery needs them. The detective uses them to solve his case. All fairly straightforward.
Hm, perhaps not quite so much when you are writing a mystery — and here we specifically do not refer so much to thrillers as they rely on action rather than clues: In a thriller, it is usually quite clear what is going to happen. The role of the protagonist is to stop it from happening.
Mysteries, to the contrary, keep the sleuth – professional or amateur – on their toes, trying to work out what has happened. In most stories, both the perp (who) and his/her motives (why) are important.
Okay, what has that got to do with clues? Well, just like the detective, readers of mysteries like to work out for themselves what happened. And you better give them a chance to do that. Otherwise, they won't like your story, go away and never come back.
Which we don't want to happen.
So, we need to give them a chance; we need to give them clues. They have to be sprinkled throughout your story in such a fashion that you also don't give your plot away. For your readers won't like that either.
A clever trick is to have vital clues appear right at the beginning when the reader is not used to the story or the characters. Your reader is trying to get into the flow of it all and might well miss a few pointers. Later, they will be a lot more "clued-up". So, if you have vital information related to your mystery, show it at the beginning.
Example: One of the murder victims has a key to a bank vault which the killer wants to break into. You can show that hanging around her neck, or the person playing with it at some time before the murder happens. When this person is found clobbered, and a chain ripped from their neck the clever reader might connect the dots. Given that you have a lot of novel between them, your reader will be happy.
Example 2: A killer commits his dastardly deeds because he doesn't like the coffee in the local coffee shop. So, you could have this person stomp from the coffee shop complaining about the filthy brew. Right at the end, it is revealed that this guy took his aversion to the local produce to an extreme. Those are just examples.
And you will need more clues throughout your story that, taken together, give you the perp and the motive. Another good trick is to have unreliable witnesses come forth like small children. No way was there a man scaling the wall at night. Kiddie has been dreaming. Only, there was ...
If you want to write a gripping mystery,that keeps your readers turning pages, you need to plot not only your story; you also need to work out WHERE to drop your clues.
Some at the beginning as we said. Others will come as you write on, when your sleuth looks at suspects (usually you start with quite a few of those), evaluates the evidence and excludes one suspect after another. And it's always the clues that make it possible.
To make it a bit more difficult, and more realistic, you also use what is called "red herrings." It is claimed that fugitives used to rub stinky fish across the soles of their feet (gross!) to get the pursuing bloodhounds off their tracks. I often wonder where they found their herrings when they were on the run but never mind.
Anyway, when writing a mystery, you're the fugitive, and the readers are on your track. They want to work out your plot and want to keep them reading.
So, you come up with false conclusions and have your detective go round in circles.
In the example of the coffeehouse case, the owner of the coffeehouse might have owed the local shop keeper a lot of money, and the detective is in hot pursuit, thinking the shop owner might have gone round the bend and offed the coffee house person. And that coffee house owner could also have an illegitimate child who came back and got rejected. Another red herring but your detective has to follow all these leads.
So, you need clues that lead towards the murder, but you throw a barrelful of red herrings into the mix, to avoid people sussing it out too early.
If you're successful, it is REAL fun to see how your readers are flitting about, trying to put the clues together and come to conclusions. Which – up until the last third of the novel, should be wrong. In the third act (you all know about the third act, right?) you can then pull everything together and, if they have been observant, at some point the readers should hit their foreheads and go "Duh".
But that better not happen before the last few chapters.
Happy plotting and clue planting!