Loretta Chase's first novel copyright 1987.
From the book flap:
Wealthy Isabella Latham is a sensible, rather mousy-looking "spinster" of twenty-six who comes, against her better judgement, to London to chaperone two young cousins for their come-out. She doesn't see herself as a candidate for the Marriage Mart, but others, drawn by her fortune, do. Among these is Basil Trevelyan, an attractive, devastatingly charming rakehell with a mountain of debts. His pursuit of Miss Latham first annoys, and then alarms, his cousin, the handsome and chivalrous Earl of Hartleigh, and the insistence of Hartleigh's little ward, seven-year-old Lucy, that she wants "Missbella" for a mama spur Hartleigh's own efforts toward winning the lady.
Basil, however, beseiged by creditors, is desperate, and he stoops to quite ungentlemanly lengths to win the wealthy Isabella's heart. In the process, one or two skeletons in the Latham family closet are set to rattling, and Isabella and her beaux become the talk of Society, setting off a wave of gossip which soon swells into a major scandal. Caught in the middle, Isabella finds herself losing her heart to one cousin as she promises herself to the other. Some snobbish relatives, her languid and thoroughly intriguing mother, Maria (herself the victim of an early scandal, which has survived to touch Isabella), and a cast of amusing characters contribute to the charm of this story of love, greed, and misunderstanding in the Regent's colorful London.