Mary Balogh 
Then Comes Seduction [EPUB ebook] 
Number 2 in series

In a night of drunken revelry, Jasper Finley, Baron Montford, gambles his reputation as London’s most notorious lover on one woman. His challenge? To seduce the exquisite, virtuous Katherine Huxtable within a fortnight. But when his best-laid plans go awry, Jasper devises a wager of his own. For Katherine, already wildly attracted to him, Jasper’s offer is irresistible: to make London’s most dangerous rake fall in love with her. Then Jasper suddenly ups the ante. Katherine knows she should refuse. But with scandal brewing and her reputation in jeopardy, she reluctantly agrees to become his wife. Now, as passion ignites, the seduction really begins. And this time the prize is nothing less than both their hearts….