To Catch an Heiress — Julia Quinn

WHAT'S AN HEIRESS TO DO?
When fetching Caroline Trent is kidnapped by Blake Ravenscroft she doesn't struggle to elude this dangerously handsome agent of the crown. After all, she's been spending most of her days running from the unwanted marriage proposals of her guardian's nitwit son. Yes, Blake believes she's a notorious spy named Carlotta de Leon, but, for six weeks until her twenty-first birthday, when she'll gain control of her fortune, hiding out in the titillating company of a dark mysterious captor is convenient--and romantic.

WHO'S A SPY TO LOVE?
Blake Ravenscroft's mission is to bring "Carlotta" to justice, not to fall in love. His heart has been hardened by years of intrigue and the loss of his beloved fiancee. But this little temptress proves oddly disarming and thoroughly kissable, and suddenly, the unthinkable becomes possible--that this mismatched couple might be destined for love.