Lord John and the Private Matter (Lord John Grey #1) by Diana Gabaldon

In her New York Times bestselling Outlander novels, Diana Gabaldon introduced millions of readers to a dazzling world of history and adventure — a world of vibrant settings and utterly unforgettable characters. Now one of these characters, Major Lord John Grey, opens the door to his own part of this world — eighteenth-century London, a seething anthill of nobility and rabble peopled by soldiers and spies, whores and dukes. Great Britain is battling France for supremacy on three continents — and life is good for a soldier.