So, you've got a great hero, wonderful plot, all kinds of suspense, all kinds of action, all kinds of twists, yet it doesn't click. Why? Maybe you need to "Put a Girl In It," as Brooks & Dunn sing, accompanied by Reba McIntyre . Or, in the case of a heroine, put a guy in it.
The fact that Harlequin's sales are up, despite a flagging economy, tells you something. People are fascinated by stories that include love and/or sex. Adding that aspect to a mystery provides one more dimension to a character and increases what's at stake.
How much you include is your choice. Or, maybe you still would still prefer your character to brave it alone.
What's your opinion? Do you enjoy mysteries with a love interest involved or not? Why?