Then Came You by Lisa Kleypas

A woman with a secret . . .
Reckless beauty Lily Lawson delights in shocking London society. She will break any rule to get what she wants . . . and she is determined to stop her younger sister from marrying Alex, Lord Wolverton, a handsome and arrogant earl who has vowed never to fall in love.

A man who will do anything to possess her . . .
To Alex’s fury, the headstrong hellion presents a temptation he can’t resist. He vows to make her pay dearly for her interference—with her body, her soul, and her stubborn, well-guarded heart.

As Alex and Lily challenge each other at every turn, they are caught up in a white-hot desire that burns through every defense and exposes the mystery of Lily’s past . . . and together they discover that love is the most dangerous game of all.