Charming the Rogue. Wright Bastards, #4

Fearless and bold, she'll forge her own path. Cailleach Claybourne knows exactly what she wants; independence, purpose.and one man above all others. To achieve the life she desires, she must navigate protective older brothers and a society that forbids young ladies any experience worth having. But she's clever and resourceful. And even though the man she's been half in love with since she was seventeen is suddenly back in town, doesn't mean he can start telling her what to do.
  There is one line he cannot cross. Bishop Black has returned to London with one goal; use the fortune he earned abroad to create a social club unlike any other. Unfortunately, his years away did nothing to cool his attraction to his former employer's intrepid younger sister. In fact, he's even more intensely drawn to her, especially when he discovers her penchant for frequenting places a young lady should never go.
Someone has to keep her out of trouble. Forbidden desires force loyalties to their limits. When the discovery of an old family secret leads Cailleach on a mission of personal importance, she can't risk having her activities disrupted by Bishop.no matter how badly she craves his kiss. He claims his interference is strictly out of loyalty to her brother. Yet the more fiercely he denies his passion for her, the more intensely she sees it burning in his eyes.