One of the decisions which needs to be made in a story (I’m thinking of mysteries, of course, but this is a general issue) is whether to make characters realistic or fun.
(This post is, in a sense, related to my post Sympathetic Suspects In Murder Mysteries, but it’s not really the same subject.)
I do have to admit that I am cheating, slightly, when I pose the dichotomy of fun versus realistic. There are fun characters who are realistic; what is unrealistic is really the presence of more than one such character in a story. Whatever exactly the criteria one has for a fun character—whether it’s having interesting hobbies, being wide read in literature, being a wit, etc.—such people are, simply, rare. People are, on average, average. That is no slight against them; God evidently likes many variations on a theme—just look at The Lessons of Beetles.
Anyway, when the question is posed, “should I have interesting characters or realistic characters” the answer is almost self-evident. (Despite having a central conceit as unrealistic as a Franciscan order of consulting detectives, I suppose I still have a hangup about realism that I’m working my way through.) The real question, I guess, is how to make the interesting characters seem realistic.
To some degree I think that the answer is to commit to them. From afar they will seem improbable. However, everyone is normal to himself so if we actually get to know the character sufficiently his odd point of view (that he’s not odd) will tend to rub off on us.
The other important thing, which is really another form of committing to the characters, is to follow through with what makes them interesting. That is, not merely to add it in for spice, but to actually make use of it and even to consider what sorts of things such an interesting person would under the interesting circumstances we’ve put them in. That said, a murder mystery tends be something of an equalizer. As Chesterton observed human beings are most like each other in the great events of their lives—birth and death and so on. I suppose that murder mysteries make life easier on the author this way, that we can throw in interesting characters and they’ll act much the same as any other, except they’ll do it in a more interesting way.