Perhaps only in the rococo court of Louis IV could the remarkable career of the Chevalier D'Eon have evolved. D'Eon, the first of Louis' secret agents, had a peculiar psycho-physical make-up that allowed him to successfully execute one of the most unusual assignments in history. His first mission was to Moscow where he spent six months as one of the Empress' ladies in waiting and became an intimate of Empress Elizabeth influencing her favorably to France. The following description was made of him at that time: ""D'Eon was young , small in stature, full-breasted and with the sort of legs that were favorable to his disguise. "" Subsequent years found D'Eon a courageous commander, expert fencer, diplomat, erudite, man of letters and wit , and also eccentric and violent. But the curse of his "" ""attractive womanliness"" brought him ultimate scandal and the recurring questions and wagers made about his sex prompted the King to order him into feminine attire in which he spent the last 33 years of his life. The mystery of his sex was not solved until after his death. Miss Nixon, a specialist in this area, (Voltaire and the Callas Case) avoids the sensational and the psychological, i.e., ""for reasons best known to himself"" almost to the point of becoming stilted. But she is a competent, exacting historian and this is , first of all, a portrait of a complex era.