Something About Emmaline by Elizabeth Boyle

Alexander Denford, Baron Sedgwick, is a gentleman to be envied. He lives a rakish life of well-celebrated ease and contentment and has one person to thank for his perfectly ordered existence—his dearest wife, Emmaline. She never complains about his mistresses or his penchant for late nights out. His friends are envious, but they don't know the truth—Emmaline doesn't exist. But when he starts receiving bills from London for clothes, shoes, hats and a staggering amount of other female accoutrements, he realises something is decidedly amiss.

Posing as Emmaline isn't a stretch for the newly arrived Lady Sedgwick, she's been conning gentry for years. But as the popular baron's wife, she now has the one thing that has eluded her—entree into London's inner circles. Against Alexander's better judgment, Emmaline is impossibly fixed in his life. And suddenly Emmaline is challenging him to be the husband she deserves.