What a trouvaille--a journalist discovered, in an antique store in Budapest, and bought for two hundred dollars, two diaries which transcribe the ten-year liaison (begun in 1895) between Princess Louise of Coburg (daughter of Leopold II of Belgium; sister-in-law of Emperor Franz Joseph--both of them amoral and unfeeling) and the Croatian lieutenant, an Austrian Uhlan, Geza von Mattachich by name, with whom she fell in love. Her imposed marriage to the brutal Philip, the Emperor's brother, had been a disaster from the start. She had also had a more discreet affair with Rudolf, of the unforgettable Mayerling story, whom she had married off to her sister Stephanie with little success. The stuff then of elegant indiscretion which began in a private room at Sacher's and ended in pilloried scandal and tragedy. Here the two diaries--hers in French, his in Croation--have been seamlessly connected (a few footnotes might have helped). They trace her expulsion from court and exile in Paris where she quickly overspent her means going into bankruptcy (she owned 125 parasols), forged her sister's signature on a note, was repudiated everywhere without a guilder, and finally fled with Geza to Croatia where even his mother refused them sanctuary. Philip harassed them further: garrison arrest for Geza; an enforced stay in a clinic ""for imbecility"" for Louise until Geza, with help, effected their escapes. Ultimately he died in her arms in Paris; she went to a lonely, dingy death in Wiesbaden. . . . One would like to know more about the participants than they reveal about themselves but the lesson in an age of flagrant royal misconduct is dismissively spelled out to her by Bertie, the Prince of Wales, to whom she appealed as a supplicant: ""It's all a question of appearances"" which she had so casually ignored. Perhaps no more than one of these Sachet whipped cream indulgences, but an imperious, fetching story which glides down the rear staircase of history--wrong-headedly, whole-heartedly romantic.