This page isn't going to be an apologia for detective fiction. Instead, if you wish, it will give you a quick and easy introduction to the formula of mystery fiction in general. This is akin to giving you a recipe for no-fail brownies. While you will turn out brownies each time with this formula, in order to win the bake-off, you're really going to have to add something of your own. The only warning is, don't tinker too much with the recipe. One or two tweaks per product will work, too many and you may end up with a bodice-ripping western, or (shock, horror, probe) a mainstream novel.
Why listen to me? Oh I don't know, why listen to anyone? However, my credentials include: two mystery novels, a mystery review column which ran for ten years in a major newspaper, and a Masters degree on the subject. And hey, *smile* normally I get paid to do this. Best of luck. I hope you find something useful here.
To paraphrase Raymond Chandler, good mystery novels have much more in common with bad mystery novels than good novels have in common with bad novels. The trick to raising your genre novel out of the morass of all that has gone before is to create a believeable and fascinating detective (your hero, and the character with whom your readers will identify); and to conjure up a vision of a new setting in which to situate your plots. The plots themselves are secondary, since when all is said and done, they've all been done before. This is not necessarily a bad thing. Your reader knows what to expect, is already halway to becoming your "ideal reader" and is more able to jump right into your world as a result.
Your Detective should be/have:
a) a loner
This is necessary to the believeabilty of your mystery in various aspects. For one thing, the detective must necessarily be the "other" to allow him/her an objectivity on the scene. There will also come a time when your detective will need to put himself (I'll just alternate gender willy-nilly throughout this diatribe, okay?) in grave personal physical danger. You will lose your reader's sympathy immediately if your character is walking into a bullet at the same time he is supposed to be picking the kids up from an after-school program. If you HAVE to give your detective a spouse, make sure the significant other has a good job, so that if your detective dies in the line of action, they will mourn, but not starve.
b) curious
You've heard the adage "show, don't tell" a bazillion times, right? Well, the best way to show that your detective is the curious sort, the terrier type of person who just HAS to know the answer, put her in a job/career that seems to attract curious types. Make her a photo/journalist, a scientist, a researcher, a librarian, a graduate student, a trained reader of some sort...you get the idea. Not only will this works as a shorthand for your readers to accept your detective as the sort who will pursue the quest; these jobs will also often lead to interesting plots. While it may be possible to have a highly curious garbage truck driver as a detective, it's more trouble than it's worth to make your readers believe this character as THE one to connect with.
c) abilities and resources
Consider your detective's JOB. Will it allow time out to go solve a puzzle? Is the mystery ON SITE? Can the mystery take place over a weekend? Or a summer holiday? Is your detective INDEPENDANTLY WEALTHY? (we pause for brief guffaw). There is so much that is distinctly "unbelievable" in mystery novels (how many people trip over seven bodies a week?) that anything you can centre in reality is to your reader's credulity comfort.
Your detective has to be STRONG. She will be in personal danger at some point in the novel. Even if you have her jogging regularly, or taking a dance course, the thought that she can endure a swim in icy water, or high kick a gun away, or wriggle out of constraints will be easier to buy.
Think of the hobbies and skills that will help. Is he a computer whiz? Can she read lips? Does he understand Serbo-Croatian? Not all these traits will be necessary in each novel, but laying the groundwork now can be helpful.
Friends of your detective should be useful. All detectives should have one pal in either the police force or Dept of Motor Vehicles; lawyers and research librarians come in handy. If you want a really violent world, a doctor is a good person to know as well.
d) a sense of morality
This doesn't mean they have to volunteer to teach Sunday School. However, again, in the words of Chandler, your detective has to be the "best man for his world, and a good enough man for any world". We have to know that, if offered a bribe by the badduns, she won't accept it.
e)needs to find the solution
To avoid a sense in which the detective is seen as some sort of snoopy voyeur, you need to find a means by which the detective is impelled to find the solution. In police procedurals or private eye novels, this is easy: the detective is hired to do the job. They usually can't afford to give back the money they were initially hired with, and have to ove forward.
If your detective is a "gifted amateur", then the best way to ahve them continue is to make them either a suspect, or have someone they care for a suspect. If the police have determined that they have "dunnit", then no one else is looking for the real culprit. Alternately, if the detective or someone she cares about is is in danger, they also have to proceed with the investigation, regardless of the danger.
f) intelligence
This character is going to solve a puzzle. It must be believeable that they can do so. As well, since there is a curious paradox involved in reading mysteries whereby, while th reader wants to solve the puzzle, they don't REALLY want to solve it. If a detective who is an idiot solves a tremendously complex puzzle, it is a slur on the reader's intelligence (this is NOT a good thing, if you want to sell more books). Oftentimes, this is why there are second bananas to the detective, to give the reader someone to feel superior to. (Watson, Hastings, Archie, Bunter)
g) name
While you may not be concerned with having a symbolic name for your character, you should be aware that there is a tendency for this in the genre. Examine the name you've chosen, jsut in case you've inadvertantly created an odd symbol pattern for trained mystery readers to wonder at. Female detectives often have androgynous names (V.I., Kinsey, Sam, Randy, etc). This likely stems from the concept that it is an "unsuitable job for a woman", but can be a good one time gag when on upping a bad guy who is waiting for a man to arrive on the scene.
There are three possible victims to create (of course, here we are discussing the primary or first victim...in some novels that will be all you'll need), and while you'll argue with me, so be it. Kill off your ex-spouse if you want, but don't ask me to call it a novel. That is therapy. When you're done, we'll continue.
1. The victim should be someone the reader cannot stand. Snarky old Uncle George who arrives at the family reunion, insults seventeen people in fifteen pages and appears dead face down in the fruit punch in chapter three. The reader can then say "Tut tut, the game's afoot" and get on with the cerebral puzzle at hand.
2. The victim should be someone likeable but not too well-known. The reader isn't given time enough to identify with the victim, though the reader likes him/her enough to want vengeance/justice. What we are trying to avoid is a period of mourning in the reader.
3. The victim must never be a child. This is a mystery, not a slasher novel. If you want to write horror, kill seven children immediately and float them down a sewer drain. Kill a child in a mystery, and you risk losing your audience immediately. The concept of game goes out the window. If your plot requires that you MUST kill a child, do them in third or fourth in a long line, well after your reader has identified with your detective and trusts him to return justice to the land.
In most cases, your villain will be the murderer, and that is whom I will be speaking of in this situation. If by chance you decide that your murderer is himself a victim of society or somesuch, give your detective someone else to truly hate in the narrative, an idiotic boss or overling of some sort.
1. The murderer should be intelligent. He/she, after all, is presenting a seemingly insurmountable puzzle for your detective and reader. Make your villain worthy of the conundrum.
2. Decide early on whether your villain is amoral or immoral. This may dictate how many bodies you stack up. Remember, an immoral person knows that something is wrong, but decides to do it anyway. An amoral person (serial killer, for instance) believes that rules are made for others, and jsut does whatsoever he or she pleases.
3. Somehow, you should present a sense of overweening ego in your murderer. They might seem meek and mild, but they always press their trousers just so, or wear a flower in their lapel, or polish the undersides of their shoes. After all, it is the most egotistical thing in the world to consider taking another's life....this has to appear somewhere else in their psychological make up for the reader to accept them as able to commit the crime.