It is too bad that Bayer's novel of Isabelle Ebethardt follows so closely the tasteful and more subdued biography by Cecily Mackworth, published in this country for the first time last winter (p. 1215). Bayer, while having apparently read all Isabelle's works as well as those about her, admits to having added elements of fantasy to a life which was one, from the early time when she dressed up in boy's clothing before she left for the East disguised in a burnoose. Russian by birth, Moslem by choice, French by her brief marriage to a Spahi, Isabelle is seen again tracking across the Sahara, attacked and tried and facing an expulsion order, drinking and smoking kif more and more immoderately, and toward the end yielding to depressive and feverish states before she dies in that flash flood. Whereas Mackworth emphasizes the mystical aspects of her nature, Bayer accents her sensuality (""I must indulge all my cravings and give myself over to desire"") even injecting erotic exchanges with her brother Augustin. His version then is ardent and aromatic--perhaps more likely to draw the audience he has in view without forfeiting the curiosity value of this dualistic, failed romantic.