Lady Lawless by Scarlett Scott

Tilly, the widowed Duchess of Longleigh, finally has everything she wants. Everything, that is, except for the forbidden man who stole her heart and fathered her child before disappearing from her life. Time has passed, but she has not forgotten him. Nor has she stopped longing for him. But when he mysteriously reappears in London, a ruthless stranger has taken the place of the lover she thought she knew.

Bedding the duchess was meant to be a job for Adrian Hastings and nothing more. The terms were simple: a month-long affair in exchange for the funds to start a new life far from the rumors and scandal tainting his past. He never intended to fall in love. Nor did he reckon on the betrayal that would almost cost him his life.

His return is with a sole purpose in mind, to gain his vengeance on the heartless widow. He won’t stop until he reveals her deepest, most shameful secrets to the world.
Unless she destroys him first.