The Duke Says I Do: Scoundrels of Mayfair Book 4 - Anna Campbell

She's impossible - and everything he wants!
In a world that doesn't care, Lady Portia Frain dedicates herself to rescuing mistreated animals. When the bully who runs a dogfighting ring threatens her, the Duke of Granville is her only hope - and the last man she wants to turn to. Not only is he the suitor her sister jilted under scandalous circumstances, he's also, in her words, "the most boring man in Britain."
Except it turns out, now she's forced into his company, the duke isn't nearly as boring as she thought. Especially in close quarters. Very close quarters.
Alaric Dempster, Duke of Granville, never wants to encounter another Frain again as long as he lives. They're nothing but trouble, including his former fiancée Juliet and her featherbrained sister Portia.
But when London's perfect gentleman stumbles upon Portia in a dangerous confrontation, honor requires him to step in, whatever his opinion of the lady in question. Things should end there, but instead Granville's orderly existence disintegrates into a shambles of secrets and kisses and far, far too much Portia Frain. Although, to his irritation, he's forgetting how much she annoys him and remembering how beautiful she is. It's a devil of a dilemma for a duke determined to keep his distance - and his sanity.
Portia and the duke are the worst possible match - which means they might just be perfect for each other!