Secrets of the Heart by Candace Camp

Rachel Aincourt fears that she’s trapped in a loveless marriage. Her husband, Michael Trent, the Earl of Westhampton, is cold, enigmatic, and completely unreadable, and Rachel herself is miserable.

But what she doesn’t know is that behind Michael’s stiff demeanor lies a man who thrives on danger and intrigue. And now he’s been drawn into a dark, dangerous mystery—one that involves Rachel herself. To solve it, he’ll need to take on the most difficult, but rewarding, task of all: convincing his wife that he loves her.