My Scot, My Surrender by Amalie Howard

SCOTLAND, 1819. Brandt Montgomery Pierce is a bastard—and proud of it. Raised by the Duke of Bradburne, Brandt enjoys an uncommon life of privilege. Despite the mystery surrounding his birth, he has wealth and opportunity, and wants nothing more. Especially not a wife.
Lady Sorcha Maclaren, the fiery and scarred daughter of Laird Maclaren, the Duke of Dunrannoch, is desperate to avoid marriage to a loathsome marquess at any cost…even if it means risking a kiss with a handsome stranger at a Scottish border festival.

But after an innocent kiss turns into a scandalously public embrace, Sorcha and Brandt get more than they bargained for—a swift trip to the altar. When danger chases them into the Highlands, and deceit threatens to tear them apart, their only hope will be to surrender…to each other.