Independent and sharp-minded, Miss Maria Dalbrooke has all but given up on finding a suitable man, as she knows women of her ilk have never fared well in the marriage mart of the ton. But all thoughts of men flee when she learns that her father, who decodes secret messages for the military, is suspected of being a traitor and leaking sensitive information to the enemy. In her haste to prove him innocent, she's forced into a most unlikely alliance with the very man sent to ensnare him, the perceptive and strikingly handsome Captain Geoffrey Armitage.

Geoff, recently jilted by a lover and determined never to trust another woman again, nonetheless agrees to the cockeyed scheme to pretend a betrothal to Maria in order to gain unfettered access to her father. Certain the plan will help him trap the man whose leaks are playing havoc with the British troops, what he did not plan on was Maria's admirable displays of courage and loyalty, along with her very acute mind and surprising abundance of womanly charms.

Despite their mutual wariness as Maria strives to convince Geoff of her father's virtue while Geoff tries to entrap the man, an undeniable attraction and searing passion flare up between the two. And as their investigation closes in on a traitor who could be hiding among the highest levels of the aristocracy and the government, Geoff and Maria may discover that their greatest enemy is their traitorous hearts . . .