A mystery is never just a mystery. A mystery, no matter what, is a group of mysteries conspiring to make a soup of clues that all work out in the end.
I recently read Agatha Christie’s Murder at the Vicarage, which, as you can rightly deduce from the title, is a murder mystery. The murder occurs early on (at the vicarage), and the author piles clues to the rafters about who killed the poor man. Miss Marple is on the case, of course, but even she has seven suspects at a time to think about. And with the plot twists coming thick and fast, no one knows anything for sure.
Now I’m going to spoil the end with as few spoilers as possible. The murderer is discovered, after a baffling series of twists. Not only that, but in the denouement of the book, no less than six mysteries were solved, not to mention other character conflicts resolved. The murder mystery was far from the only part of this murder mystery. Indeed, in order to have as many clues as the author introduced, she had to include each of the six mysteries— otherwise it would be obvious who did it.
This, I think, is an important concept if you wish to write any sort of mystery novel: there is never only one mystery. There are several, coinciding to make this period of time worthy of being put into a book. It doesn’t matter what kind of mystery you’re writing— there is never just one.
The interweaving of all the different mysteries gives you the air of confusion that keeps each mystery from being solved at once. It also gives you red herrings that can occur without the true villain having to plant them all— as each mystery steps on its neighbor’s toes, they leave clues that muddle the scent for the next one in line. Furthermore, it creates even more tension, which is probably the most important.
In any mystery, the tension is very low because the stakes are very low. Unless you’re writing a thriller, in which the person who first murdered is intent on doing it again, a murder mystery is over once it is solved. Most of the action happens at the beginning of the book, where the character is murdered— from then on, the action consists of interviews and lots of thinking, not much action or adventure. However, there is some tension based on characters being angry that they’re suspected, or desperate to find the truth, or any other type of character conflict. But that tension is very small compared to that in any other type of story. Murder mysteries, as they are, are at a disadvantage.
This is why a murder mystery is never just a murder mystery. By putting several mysteries on top of each other, you compound their tension. All the confusion, all the suspects, jack up the tension until it’s worth reading after all. Sure, all the evidence points to this person, but what about this clue? That points to someone else, who couldn’t possibly have done it. What if the person they arrest is the wrong one? All that conflict, all of that confusion, lends to the tension of the whole story. It’s not as much as your average action adventure, but it’s enough as long as the reader is engaged early on. That, plus the conglomeration of mysteries, will lend the story its compelling nature.
While adding these mysteries, however, you must make sure to resolve each one by the end of the book. Each mystery is a promise, and the fact that these clues appear enforces the promise that they will be explained by the end. James Patterson, in Confessions of a Murder Suspect, did this remarkably badly. He had a murder mystery, and a couple other mysteries on top of that, and only resolved the murder mystery. All the other clues, which he used to create more tension and muddy the waters as I described, he let lie, perhaps leaving it for the next book in the series. That, I think, was what made me indifferent about the book. While in good mysteries everything is explained, Patterson left his mysteries unresolved except his main plot, which destroyed the ending. Unfortunate, but an easy mistake to make with so many mysteries on hand.
Don’t be James Patterson. Be Agatha Christie, the master of the multifaceted mystery novel. Stick lots of mysteries together, throw in plenty of clues, make a giant mess out of which your Holmes or Poirot or curious child (who is probably also related to either Holmes or Poirot) can discover the true perpetrator. Drive up tension, but make sure to resolve everything at the end. This, I believe, is the way to make a mystery novel work.