A mystery author is a magician. Magicians know how to entertain and draw attention away from what they are actually doing to make people think they are doing something entirely different.
Brain cramp, right?
It's really very simple.
There's the actual plot and then there's all the other "sleight-of-hand" plots that throw off readers so they don't see the truth that's right in front of them.
This is the plot that all other plots swirl around. This answers everything: who died? who is the killer? what was the weapon? when did it happen? why did it happen? and how did it happen? It's the truth of your story.
Sleight of Hand plots...
These plots are the ones you dazzle your readers with. They may answer some of the who, what, where, when, why and how, but not all of them. Some of these plots may sputter out quickly, some may last for most of the book, but they should all logically conclude.
All you have to do is pick up your "what-if" wand and start plotting.
What do you enjoy about reading/writing a good mystery?