A good villain is essential to a good mystery.

He or she is the author of the crime, the driver of the plot, and the key to solving the ensuing investigation.

Often, the more cunning and deceitful the villain, the more satisfying their unmasking and capture. This is one reason for the public fascination with fictionalized serial killers—they leave clues, have identifying signatures, and show little remorse, which gives readers the opportunity to put the puzzle pieces together and celebrate their apprehension. But serial murders represent less than one percent of all murders committed in any given year, and violent psychopaths comprise less than one percent of the general population. Few real-life serial murderers send Jack-the-Ripper-style letters making the genius serial killers largely a Hollywood invention. We might love to see the serial killer revealed and outsmarted, but they are hardly a believable villain.

And for lovers of crime fiction like myself, capturing the villain is only half of the thrill of reading a thriller. We read not only to determine who or how, but also why. We read to understand. If murder is a universal evil, why would someone commit such an irrevocable break of the moral code? Readers are like members of a jury in a criminal case—we need to know a villain’s motives before we hand down our judgement.

The motive of a serial killer is always the same—they’re driven by compulsion or enjoyment. Evil for the sake of evil. How boring!

The unintentional villain, on the other hand, is wicked by accident. They are in the wrong place at the wrong time: they’re driving through that intersection when their nemesis steps off the sidewalk; they have a short temper and grab a knife without thinking; they’re pushed by the bully one too many times and snap. They’re not taunting the police with Jack the Ripper style letters. Instead, to find them and understand their motivation, the investigator (and reader) must turn to the victim’s inner circle, examine family dynamics, and probe the psychology of friend groups, petty jealousies, and fatal misunderstandings.

Because the unintentional villain never intended to act so murderously, the unintentional villain complicates questions of guilt and innocence. On the sliding scale of good and evil, it’s easy to place serial killers at the wicked end, but where do we position the hit-and-run driver, the heavy-handed drink-pourer, the staircase pusher, and short-tempered friend? Do we judge a person less harshly if they meant to hurt their victim, but not kill them? If they acted without thinking? If they killed to protect someone else?

Dublin murder squad author Tana French is an expert at crafting these unintentional villains—a delusional young man who thinks he’s a hero, a friend who acts in a moment of angry passion, a boarding school girl who misunderstands the complexities of first love, a brother and sister duo who lure a bully to his death. Tana French weaves these tales so we understand her villains would never kill under normal circumstances. They’ve acted on misinformation, by accident, or under duress. As readers we may even hope that they evade capture or sympathize with them when the quick-witted detective tricks them into a confession.

In this way, unintentional villains force us to ask hard questions about right and wrong.  In a famous Liane Moriarty mystery, a whole community comes together to hide the murder of a wealthy banker, who’s fallen to his death at a party. In the course of the novel, we learn that the victim is not only a serial philanderer, but also a physically and sexually abusive husband. Does this make his murder justified? Should the perpetrator be judged less harshly because they didn’t intend for him to fall? But how can we ever really know what’s going on in someone else’s head?

The ambiguousness of determining intent is the starting point of Sally Hepworth’s novel The Soulmate. A family lives close to a cliff where people often come to end their lives. The husband develops a reputation for talking people off the ledge, but when a woman falls to her death, and the wife sees her husband at the cliff’s edge with his arms outstretched, she begins to question his actions. Can she believe him when he says he didn’t push the woman and instead was reaching out a saving hand? The end result is the same: the woman remains at the bottom of the cliff. But according to both our legal system and public perception, premeditation and intention matter. The different sentences for murder, voluntary manslaughter, and involuntary manslaughter underline our collective emphasis on motive.

Intent is a key question in both my debut novel The Resemblance, in which a fatal hit-and-run on a university campus leads a detective to examine the dark side of college life, and my new novel The Professor, in which a student’s suspicious death prompts the now retired detective to investigate affair allegations, classroom hierarchies, and roommate dynamics. Readers will ask: in the moment before impact, did the driver of the speeding vehicle press the accelerator or slam on the brakes? Did the professor give her student her number in order to abuse her authority or out of concern for his well being?

If a serial killer is a puzzle to be solved, an unintentional villain is a Rorschach picture to be examined. What we see in the villain reveals something about ourselves.

Few of us (I hope!) can imagine setting out to kill another person. But would we kill to protect a friend? In self-defense? In a moment of passion? What would we do in the shoes of the unintentional villain who kills someone on accident? Would we do the right thing and surrender? Or turn and run in the opposite direction? The truth is we can never know until we find ourselves in such a situation. It’s that curiosity about the unknown person living inside of all us—are they a hero or a villain?—that’s so fascinating. The unintentional villain allows us to explore the gray areas of our own moral judgements and psyches.

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