The Saint of St. Giles by Nadine Millard

Nicholas Fyfe, the Duke of Barnbury had suffered a tragedy in his past. A tragedy that he hid from the world, and which shaped him into the man he was; a man who dedicated his life to helping the unfortunate souls of St. Giles, saving them because he had been unable to save the woman he loved, and the child he’d never known.
Nic prided himself on the rigid control he had over his life and his emotions. He never let himself feel anything too deeply, and he never let anyone get too close. That was how he’d lived for the past ten years. And that’s how he intended to continue living.
Alison Langton had come to England to follow in her sister’s footsteps – meet a handsome English gentleman and enjoy the glamour and romance of a famed English Season.
Beautiful and admired by all, Alison had never met a man she couldn’t charm. Until Nicholas Fyfe. From their first meeting, the sombre duke had made his dislike of Alison blatantly clear. And the more he made his feelings obvious, the more Alison was determined to find out why.
With the Season in full swing, Nicholas finds it harder and harder to maintain his much lauded self-control around the irascible Alison Langton. And the closer he comes to giving in to the temptation of her, the closer she is to finding out his secret.
Will Nicholas finally give in to his feelings? And can Alison tempt the Saint of St. Giles to sin?