«The Dastardly Duke» by Eileen Putman

Tormented by a dark secret, Julian LeFevre, Duke of Claridge, is a notorious and dissolute rake. His half-hearted attempt to reform his character has left him bored to death. To relieve the tedium, he wagers a friend that he can mold any pretty trollop from the London streets into a lady who'll past muster with society's elite.But Hannah Gregory is no biddable lump of clay. She has solemn gray eyes, a rebellious streak — and is deaf from a long-ago accident. And although she conceals her real past, she can't conceal her attraction to the scoundrel who offers her a small fortune that could pay for a new medical treatment.The charade might heal her, but it also might break her heart — if she forgets that this dark and dangerous duke is well past the point of redemption.
About the Love in Disguise series: In these tales of Regency intrigue, nothing is as it seems: A street wench masquerades as a debutante to fulfill a rake’s wager; an actress pretends to be a vengeful lord’s mistress to catch a killer. A noble war hero disguises himself as a much older man to woo an on-the-shelf spinster. An independent widow forces her disapproving business partner to pretend to be her fiancé—and teach her about passion.All are daring masquerades, with love as the prize.