The Wallflower Wager by Tessa Dare

They call him the Duke of Ruin.
To an undaunted wallflower, he’s just the beast next door.
Wealthy and ruthless, Gabriel Duke clawed his way from the lowliest slums to the pinnacle of high society—and now he wants to get even.
Loyal and passionate, Lady Penelope Campion never met a lost or wounded creature she wouldn’t take into her home and her heart.
When her imposing—and attractive—new neighbor demands she clear out the rescued animals, Penny sets him a challenge. She will part with her precious charges, if he can find them loving homes.
Done, Gabriel says. How hard can it be to find homes for a few kittens?
And a two-legged dog.
And a foul-mouthed parrot.
And a goat, an otter, a hedgehog . . .
Easier said than done, for a cold-blooded bastard who wouldn’t know a loving home from a workhouse. Soon he’s covered in cat hair, knee-deep in adorable, and bewitched by a shyly pretty spinster who defies his every attempt to resist. Now she’s set her mind and heart on saving him.
Not if he ruins her first.