Conjuring the puzzle-mystery is a magic trick. The impossibility of a solution is merely an illusion and, when the reveal is made known—if the piece is well-written—the solution seems obvious, a perfect fit. It is up to the author, i.e., the magician, to provide the misdirection and the entertainment along the way.
This is most apparent in "locked room" mystery plots. Here, the crime seems to violate the laws of nature. For example, take one of the murders in the classic, The Three Coffins by John Dickson Carr. It has just begun snowing. A man in a heavy overcoat walks out of his living quarters and into an alley. Several passersby hear a gunshot and within seconds they arrive at the entrance to the alleyway where they see the victim collapse face first.
The puzzling part is that the victim was shot from up-close as evidenced by powder burns on the back of his coat where the bullet entered. And yet, there is no perpetrator nearby and the only footprints in the snow are those of the victim. Furthermore, with the rapid appearance of the witnesses, there was no time for the killer to have fled. So how did the murder take place?
I'll provide the answer below, but first let me delve into how I go about creating a puzzle-mystery. First, I invent a dramatic scene. Then I add a layer of what seems impossible. Then it is my task to work out a solution that is possible, sensible and, above-all, satisfying.
In my novel, Never Kill A Friend, I present a variation on the locked-room mystery. In this case, the police arrest a young man who woke up to find his brother butchered alongside him in his one room apartment. The police report that the locks to the one entrance were solid and were bolted. This is not a case where no one could have done it, instead the evidence points to exactly one person. Later, that night, the lead detective wakes to find someone similarly butchered in her home.
So, using this as an example, how do I make the impossible, possible? First of all, I do not write paranormal mysteries, so I focus on the fact that what happened obeyed the laws of nature. If these laws seem to break, then the assumptions were wrong. I tweeze apart what is solid fact and what is assumption. This leads to an essential element to attacking this type of mystery, formally called epistemology: How do we know what we know? and, the more crucial question, Do we truly know what we know?
A magic trick seems impossible because a solid object disappears from a magician's hand. But, was that truly a solid object? Was it even in his hand or could it have been switched between hands before the moment of the illusion? Next time you read a whodunit, look at the author as a master of misdirection. Avoid the distractions.
For the murder in Never Kill A Friend. (No spoilers)
Statement: The police arrest a young man who woke up to find his brother butchered in his locked, one-room apartment. The locks are said to have been solid and secured.
But: Since the police arrested the man, obviously the apartment is no longer sealed. Could someone else have been there? Could that someone have snuck out? If the police burst in, then the locks would be broken. How do they know they were they solid before that? If the young man opened the door for the police, then how do they know they were adequately bolted before that? Attack the assumption and the impossible becomes possible.
To reiterate: #1. Make the situation dramatic. #2. Make it seem impossible. #3. Take apart the assumptions and, most importantly, #4 make the solution satisfying.
The solution to the murder from The Three Coffins, for those who don't mind spoilers.
Statement: The victim was shot from up-close, there are powder burns on the back of his coat where the bullet entered.
Evaluation: It is possible that the powder burns around the entry were from a previous incident and he had now been shot and that he put on his coat afterwards. . . only no. Unsatisfying solution. The previous bullet-hole aligns with a later, death dealing wound? Still, it's always good to question the assumptions.
Conclusion: Here, the forensics stand. He was shot up-close. This is the premise on which the mystery is built.
Statement: Several passersby hear a gunshot and within seconds they arrive at the entrance to the alleyway where they see the victim collapse face first. There is no perpetrator nearby and the only footprints in the snow are those of the victim. With the rapid appearance of the witnesses, there was no time for the killer to have fled.
Evaluation: The law of physics apply: the perpetrator was not standing behind the victim when he was shot in the alley. Therefore, the victim was shot elsewhere. But, what about the gunshot? This is the faulty assumption: the gunshot which the witnesses heard was the same as the one which killed him. This is impossible.
Conclusion: The victim was shot before he left his living quarters. He walked into the alleyway, his thick winter dressing prevented blood from dripping. The second shot, which was the one the witnesses heard, was fired out of the window of the living quarters and missed.
Bio: Martin Hill Ortiz has also published under the name of Martin Hill. He lives in Puerto Rico where the mother's maiden name becomes a second surname. Never Kill A Friend, his third novel, was recently published by Ransom Note Press.