There’s almost nobody alive who hasn’t enjoyed curling up with a good detective book or other “whodunit.”
And there are just as many people who would one day like to write one. When writing one becomes the desire, knowing how to plot a mystery novel will be a skill that should be learned.
The second thing to keep in mind in plotting a mystery is to make sure what’s being written is creating a mystery and NOT confusion. Give the reader enough information to keep him or her interested and engaged in the story but not so much that they’ll tire of the storyline. Any good mystery plot is composed of a number of “what” questions such as “what will,” or “what is.” A few “why” questions, like “why did,” can also be a good thing to add.
Another thing newer writers of mysteries need to remember is to get the story moving quickly. Don’t waste time with complicated set-ups and character developments. This is a mistake. Instead, just get to the point and the meat of the matter. Additionally, spend some time thinking up a tasty moral or ethical dilemma for the protagonist and then work to get it smoothly inserted into the pace of the novel.
The last and perhaps most important element in a mystery plot is that there has to be a tension that exists between the protagonist (the “good guy”) and the antagonist (the “bad guy”). This doesn’t mean a real fistfight or the like, but rather the good guy (or girl) should be working to solve a problem and the antagonist must be working to stop the solution that will develop. Mysteries are about good and bad, in most cases.
When all five recognized elements of plot exist in these sorts of novels, the story will inevitably of a high-quality nature. Stick to these time-honored plot components and any story that results will have a fairly high chance of ultimate success