His Lordship's Swan — Martha Kirkland

AN UNEXPECTED BETROTHAL...
Unable to decide which of the ravishing Swann twins to marry, Lord Evan Trent lets a flip of the coin determine his fate, resulting in an offer of marriage to the eldest daughter. His dismay is understandable when he arrives at the Swann manor to discover he is betrothed to a woman he's never met--Lydia Swann, the third--and oldest!--Swann daughter. Evan knows the girl's father has duped him, but as a man of his word, he will honor his pledge to marry her...

...LEADS TO AN UNEXPECTED LOVE
Refusing to be trapped in a loveless union, Lydia offers her fiance a scandalous proposal. If he will allow her to spend a month at his country estate, where she can renew the acquaintance of a man she's loved since she was a schoolgirl, she will break the engagement at month's end. Yet Lydia never imagines that joining forces against her father's trickery will cause her to lose her heart to Evan, and make her blossom into a most beautiful swan...