Hellfire Mysteries Series by Anne Herries

Daneil, Earl of Cavendish, find the frivolity of the ton dull after the adventures and hardships of the Peninsular War. But boredom rapidly disappears when he's drawn into the mystery surrounding the abduction of gently bred girls. His investigation endangers his mother's new companion, Miss Elizabeth Travers. Although she is tainted by scandal, her cool and collected response commands Daniel's respect, while her beauty demands so much more.

A Wealthy Widow.

Regency. She'd put the shadows of her past behind her. .. Now Miss Sarah Hunter was delighted at the prospect of a Season in London--and at the opportunity to spend time with the man who'd once saved her life! But Mr. Elworthy was much changed. Rumors and secrets tarnished his honorable name, and the ton had begun to wonder where the truth of the matter lay. He found a staunch champion in Sarah--but as she defended him she was inexorably drawn into the mystery. .. .