These Old Shades by Georgette Heyer
Under the reign of Louis XV, corruption and intrigue have been allowed to blossom in France, and Justin Alastair, the notorious Duke of Avon and proud of his soubriquet 'Satanas', flourishes as well. Then, from a dark Parisian back alley, he plucks L-on, a red-headed urchin with strangely familiar looks, just in time for his long over-due schemes of revenge on the Comte de St. Vire. Among the splendours of Versailles and the dignified mansions of England, Justin begins to unfold his sinister plans -- until, that is, Leon becomes the ravishing beauty Leonie ... Yet again Georgette Heyer shows the qualities that made her one of the most successful and best-loved romantic novelists of her age, and why her popularity endures to this day.