A Duke by Any Other Name by Grace Burrowes

Nathaniel, Duke of Rothhaven, lives in seclusion, leaving his property only to gallop his demon-black steed across the moors by moonlight. Exasperated mamas invoke his name to frighten small children, though Nathaniel is truly a decent man -- maybe too decent for his own good. That's precisely why he must turn away the beguiling woman demanding his help.

Lady Althea Wentworth has little patience for dukes, reclusive or otherwise, but she needs Rothhaven's backing to gain entrance into Polite Society. She's asked him nicely, she's called on him politely, all to no avail -- until her prize hogs just happen to plunder the ducal orchard. He longs for privacy. She's vowed to never endure another ball as a wallflower. Yet as the two grow closer, it soon becomes clear they might both be pretending to be something they're not.