Lord John and the Brotherhood of the Blade

The first book in Diana Gabaldon's Lord John Grey series, set in the same world as her Outlander novels
It's 1758 and Europe is in turmoil - the Seven Years War is taking hold and London is ripe with deceit. The enigmatic Lord John Grey, a nobleman and high-ranking officer in His Majesty's Army, pursues a clandestine love affair and a deadly family secret.
Grey's father, the Duke of Pardloe, shot himself just days before he was to be accused of being a Jacobite traitor. Now, seventeen years on, the family name has been redeemed; but an impending marriage revives the scandal. Lord John knows that as Whitehall whispers, rumours all too often lead their victims to the wails of Newgate prison - and to the gallows.
From barracks and parade-grounds to the bloody battlefields of Prussia, Grey faces danger and forbidden passions in his search for the truth. But it is in the stony fells of the Lake District that he finds the man who may hold the key to his quest: the enigmatic Jacobite prisoner Jamie Fraser.
Eighteenth-century Europe is brought startlingly to life in this compelling adventure mystery.