Say You Love Me by Johanna Lindsey
Kelsey Langton has been left penniless by her parents' death, and as the sole provider for her younger sister, Jean, she needs to find them both a home and a future. There seems to be only one way to ensure Jean's well-being, and that is by sacrificing her own - Kelsey decides that she must sell herself to the highest bidder. With fear and trepidation she enters the House of Eros, resigned to become the plaything of some well-heeled gentleman. The man to win her is Lord Derek Malory, a dashing rakehell from a family of harming London rakes. Enchanted by the stunning, dark-haired girl with flashing bright eyes, he purchases her for his mistress, sweeping Kelsey into a world of astonishing family secrets, perilous rivalries and unconventional loyalties. But Lord Derek is unaware of the true worth of the prize he has so frivolously acquired - never dreaming that his proud, spirited mistress is a highborn lady blessed with grace, wit and intelligence as well as beauty. And he certainly never expected that he would fall in love with her.