The Mistletoe Mistress by Maddison Michaels

Notorious rake, Michael Drake, the Viscount Blackthorn accepts a Christmas wager to be the first to seduce the next lady to walk under the mistletoe, but the lady turns out to be none other than Holly Jenkins; a woman from his past, whom he has sworn to protect, but whose bold antics drive him to distraction…and temptation. Can he protect her from himself?
Holly is living a lie. Forced to masquerade as a widow to keep herself and her sisters safe, she earns a living helping those being undeservedly blackmailed by using her lock-picking skills to expose the villains behind the schemes. Attending a ball, her clandestine work is interrupted by Lord Blackthorn, a man who is as vexing as he is sinfully handsome. A man who she’s always had feelings for, which she understands are futile. Because everyone knows you can’t give your heart to a rake… Or can you?
But Michael has his own secrets, ones serious enough that could threaten any chance they have of a future together. After all, lies and deception. have a dangerous habit of unraveling when one least expects it…