The Condor's Head by Ferdinand Mount
A fair-haired young man from Virginia sees a dark girl rowing on the lake at Versailles and he falls in love. She turns out to be the Duchess de La Rochefoucauld, known as Rosalie, married to a man twice her age who also happens to be her uncle. It is the spring of 1875 and the young American, William Short, nicknamed Wm, has crossed the Atlantic to serve as secretary to his adoptive father Thomas Jefferson at the Paris embassy. Lodging on the Champs Elysees with Jefferson's two young daughters and their teenage slave Sally Hemings, Wm becomes the darling of the free spirits of the ancien regime, who want to copy everything American, including revolution and the pursuit of happiness. But this is a time when nothing runs straight, certainly not the pursuit of happiness. Together and apart, Wm and Rosalie endure the bloodiest days of the Terror when everyone loses their heads or their illusions except for one man, but that man is about to become President of the United States. Stylish, intelligent and witty, "The Condor's Head" is by turns tense and erotic, incredibly funny and unbearably sad. It includes the real-life letters of Wm and Rosalie and Jefferson, some never published before. It also incidentally reveals the truth about the Third President and Sally Hemings.