Duke in Darkness by Nicola Davidson

Colonel Gabriel Jordan-Ives once lived to serve king and country, with high hopes for a future of love, marriage, and children. Now he exists as a poor recluse, haunted by horrific war memories and struggling with a maimed body—until the day he unexpectedly inherits his cousin Exton’s dukedom and must leave his sanctuary for London, rejoin the ton he cannot abide…and secure the line with a legitimate heir.
Often punished for her hot blooded, curious nature, Lady Lilian Nash transformed herself into the perfect duchess-in-waiting to please her family. However they demand more—wed her late fiancé’s mad cousin—or they’ll be financially ruined. Her marriage of convenience is confusing; Gabriel is unlike any man she’s ever met, an untamed aristocrat both generous and secretive, a scarred yet powerful husband who introduces her to wicked pleasures in the bedchamber even as he forbids her from touching him.
But as the brutal shadows of his past intrude on their present, and cruel enemies attempt to destroy a growing bond, can love save a duke in darkness, or will the shadows consume them both?