A great unsolved mystery in American political culture is what became of the U.S. Congress's state portraits of Louis XVI and Marie-Antoinette during the British invasion of the Capitol, Wash., D.C., on the night of 24-25 August 1814. These were official full length images of the French monarchs arrayed in ceremonial magnificence. The fate of the royal portraits has been difficult to determine. Larkin undertakes a comprehensive examination to test...