I promised Mary-Frances I'd say more about this, so here goes ...
A couple of years ago, I interviewed editors and agents for a column I used to write for a mystery writers publication. Almost all of them said that one of the biggest problems they find in manuscripts by new mystery writers is that the detective does little or no detecting. "Detective" is used here in an informal sense -- the protagonist of the mystery, whether or not he or she is with law enforcement or is a private eye.
Now, to readers, this might seem like a problem that should be obvious to a writer, but it is easy to let it creep up on you when you are the person creating the work word by word, line by line, page by page.
It's especially easy to turn your detective into what I call the Serial Interviewer — the Serial Interviewer is nearly as common in crime fiction as the serial killer, and to my mind, just as deadly when it comes to reader interest. This is a detective who never really solves anything or puts two and two together. Throughout the book, he spends most of his time visiting other characters and talking to them. Bit by bit, they tell him everything. Eventually, someone tells him who committed the murder. Quite often, it's the murderer himself, confessing — holding a gun on the hero, no doubt. He'll be foiled at the last moment, but not before he supplies all the answers for the idiot in his gun sights.
You should try to come up with something a little better than the Serial Interviewer.
By no means am I suggesting that your detective shouldn't question witnesses and others. She can meet intriguing (and possibly guilty) characters, and you can increase tension in the book through these encounters. We can see her act as an observer of persons and their habits.
There's a fine old tradition of this sort of thing in the mystery novel, and some of the best humor in them has come from such encounters. Alas, it often seems as if the people who love the witty observations and repartee of Chandler's Marlowe and Hammett's Continental Op have failed to notice that both characters also solve crimes. They do talk to lots of folks, skewer some, and snap out comebacks -- but they also do some real thinking.
A detective needs to notice things other characters aren't seeing — and at the end of the day, we shouldn't be wondering if all the other characters have missed clues because they are walking while comatose. A detective has to draw conclusions others might reasonably fail to make. He or she should be actively involved in solving the crime -- not passively collecting solutions. Even an armchair detective like Nero Wolfe is more active than passive -- he uses his mind, has the ability to sift through information to arrive at a logical conclusion. Ideally, the reader has also had the opportunity to observe and gather information at the detective's side, but hasn't necessarily recognized the significance of important clues.
(If you're writing a book of suspense or a thriller, some of your tasks may be different than those of writers of detective fiction. That doesn't mean your hero should be passive, though.)
This business of the detecting detective is also one of several reasons why learning about forensic science is a starting point rather than an ending point for writing a mystery novel. Simply having an unusual idea about how someone might be killed or having an idea for a single clue or piece of evidence is nowhere near what you need to write a novel. Among many other obligations to your reader, you have to figure out how the detective will find the key to the meaning of the evidence. You also have to make it clear how the detective arrived at an answer when others didn't.
So look through that manuscript before you send it off, and ask yourself if your detective is carrying the story forward, or simply being swept along on a tide of readily available information. If you work to make the hero more active, you'll increase the possibility of selling your book.
Just my opinion on the matter — in the end, you get to try it your way.
Photo above courtesy of Clarita, who kindly made it available on morguefile.com.
