When it comes time to write a good mystery novel, most people focus on the characters and getting them from point A to the end of the books. The book needs to have enough suspense and suspicious characters so that the answer isn’t obvious, but also needs to be relatively simple so the reader doesn’t get lost among all the sub-plots.
However, many a mystery author has left one thing out of their narrative that will make any mystery hard to put down. Reader involvement.
While you as an author don’t need to hold the reader’s hand throughout the entire story, you should allow them to piece together the mysteries of the story as their detective does. Have several suspensions characters with sketchy alibis and interesting motives, and give several possible ways for the crime to have happened.
The reader should be just as puzzled as your detective is when it comes time to sit down and collect the evidence, or maybe some readers with a knack for deduction will start to solve the crime themselves and then wait to see what happens and if they were right.
You never know what will make a reader get that aha moment and really understand the book, and it will make them read the book even faster. Contrary to popular belief, getting the ending of the book before the end is good for a mystery.
Your readers are often reading mysteries because of an interest in them, so indulge that interest and turn them into detectives as they read along. Give them a crime and have them figure out who did it, or give them the who and have the figure out how the crime was done. Write with your reader in mind, and no one will ever be disappointed.