Noble Scoundrel - Peril & Persuasion, #1

To protect a daring young lady and her brother, he must defeat his villainous past or lose the only thing worth fighting for. A Shameless Scoundrel. Hardened by a violent past, Mason Hale is a feared and ruthless scoundrel of London's East End. But to pay off a personal debt, he agrees to employ his skills as an undefeated bare-knuckle boxer by becoming a young duke's bodyguard. A Dauntless Lady. Lady Katherine Blackwell's only concern is keeping her brother safe while she figures out who is behind the repeated attacks against him.
She can't risk being distracted by the brutishly handsome man who challenges her at every turn. A Threat Too Great to Fight Alone. As the enemy closes in, Katherine and Mason discover a plot far more sinister than they imagined. And though Lady Katherine insists she doesn't need a hero, Mason is surprised to discover that's exactly what he wants to be.