An Outlaw’s Desire by Catherine Kean

Days before Christmas, Pitt Rutherford is blackmailed into planning an attack on Millenstowe Keep. He discovers, however, that Lady Blythe Welborne, the only woman he’s ever truly loved, is within the castle’s walls.
As the attack draws ever near, Pitt must choose whether his obligation to claim a legendary treasure is worth more than a second chance at true love.