To Woo and to Wed by Martha Waters

The final installment in the Regency Vows series follows the heir to a dukedom and a young widow, once very much in love, as they reunite years later to fake an engagement for the benefit of her sister.

West, the Marquess of Weston, and Sophie, Lady Fitzwilliam Bridewell, have lately been spending a considerable amount of time together. But West and Sophie are not new acquaintances. In fact, years ago, they had once been nearly engaged until West’s almost fatal curricle accident and his meddling father threw them off course.
Now recently widowed, Sophie has put aside all thoughts of romance. But when her widowed sister, Alexandra, mentions a fondness for an earl, Sophie realizes that she may be holding her sister back. Alexandra won’t move forward with an engagement until Sophie, too, settles down again, and so Sophie approaches West with a plan. They will announce their engagement and break things off once Alexandra is happily married. It’ll be simple. After all, it’s not like she is going to fall for West a second time, not when Sophie has sworn not to risk her heart again.