Temptation is as old as Adam and Eve. Unfortunately, succumbing to it is as natural as breathing to the gentlemen in the haut ton. To save prospective brides bent on fidelity, three friends will discern the faithful from the philanderers. What they hadn't counted on was emotional entanglements. Catherine Rutherford has been smitten with the sinfully handsome American, Lucas Beaumont, since their introduction the year before. And he appears just as enamored of her, for following his return to London he launches a seductive campaign to ensnare her heart and capture her hand in marriage. Never has Catherine been so confident in the outcome of a courtship.that is until she discovers Lucas was in love with her sister first.

Although she and her twin share the same face, Catherine refuses to share a man's affections much less be any woman's substitute. So with the aid of her twin and two friends, she challenges the man she loves to the ultimate test of fidelity. Posing as her heartbroken sister-who is really anything but-Catherine seeks his solace from an "unhappy marriage" and begins a tempestuous game of seduction where the true proof of his love lies in his ability to resist her charms.