World of Love by Barbara Cartland

Almost in a heartbeat demure soon to be a debutante Carmella Bramforde plunges from virtue into a High Society world of lies, deceit, adultery and worse.
Dressed to kill and made up as one of the notorious professional beauties, she plans to burgle the Marquis of Ingleton's house party to retrieve the family heirloom her brother Gerry lost at cards.
Horrified by the depravity and vice, Carmella dices with death at the hands of a genuine burglar.
The question is can love save her from sinking further into this sordid and seamy world?