A Most Dangerous Profession (Hurst Amulet Series) By Karen Hawkins

For beautiful, seductive Moira MacAllister, the stakes have become terrifyingly high. Her daughter has been abducted and a priceless ancient relic is the ransom. Moira must acquire it at any cost, even if it means confronting the man she once duped and left, a man who still doesn't know she has a child . . . and that he is the father.
Robert Hurst, an operative in the king's service, has never forgiven the mysterious spy who seduced him into marriage and then disappeared without a trace. Now, as he pursues the onyx box that will save his brother's life, their paths cross again. But Robert isn't sure which he longs for more—to satisfy his lust for revenge or to quench his relentless hunger for this bewitching woman.
When Moira reveals to Robert her long-kept secret, however, he realizes his burning desires must wait as a treacherous foe closes in, threatening all they hold dear . . . and their second chance at love.