Lord John and the brotherhood of the blade
(Book)

Series information from Fantastic Fiction.

It's been seventeen years since Lord John's late father, the Duke of Pardloe, was found dead, a pistol in his hand and accusations of his role as a Jacobite agent staining forever a family's honor. Now unlaid ghosts from the past are stirring. Lord John's brother has mysteriously received a page of their late father's missing diary--and John is convinced that someone is taunting the Grey family with secrets from the grave. So he turns to the only man he can trust: the Scottish Jacobite James Fraser. But war, a forbidden affair, and Fraser's own secrets will complicate Lord John's quest. Until James Fraser yields the missing piece of an astounding puzzle--and Lord John, caught between his courage and his conscience, must decide whether his family's honor is worth his life.