The Devil Himself. The Devil You Know, #1

Owner of the Devil's Playground, a gaming establishment and pleasure club, Rys Grey has given up ties with his aristocratic family after a falling out with his father. His brother Owen is the marquess now, and Rys is happy with his life, running his club and staying out of family politics. At least until an old family friend arrives to tell him his brother has been killed. Lucian Fitzwilliam has been friends with Rys's older brother since childhood, and when Owen is killed, he fears for the safety of his wife and children.
So he goes to Rys to help him find out who killed Owen, and how to keep everyone safe. Rys has no intention of helping, but Luc has always been the one he couldn't have, so he agrees to help simply to keep the man close. As they work to discover Owen's killer, Rys and Luc find family intrigue, danger, and each other. But can they solve the mystery of Owen's death before the killer comes after them, or will they lose the game, and each other, for good.
This is a MM regency era romance with action adventure elements.