Persuading Patience by Emma V. Leech

Lord Percy Nibley needs a wife, preferably before his mother’s nagging on the subject drives him to distraction. But being more comfortable with his rock collection than flirting, he’s not having a lot of luck.
In desperation, the shy nobleman enlists the help of Baron Marchmain – Lord August Bright. August is nothing short of dazzling. Charming, witty and amusing, he’s the darling of the ton, and a notorious heart-breaker.
August selects a suitable young lady for Lord Nibley; Miss Patience Pearson, a cool, level-headed woman, close to being on the shelf and with the reputation of a blue-stocking, meanwhile setting his own sights on capturing the heart of her vivacious younger sister, Caroline.
But Patience is not easily charmed, guarding her sister with the tenacity of a lioness and August must be at his most devastatingly charming to get past her defences.
Having finally done so, however …
August isn’t at all sure he’s chosen the right sister.