Best known as the author of the classic ''Darkness at Noon'', Koestler was one of the most influential and controversial intellectuals, involved in and commenting on almost every political movement of the twentieth century. As young man, he was a committed Zionist and moved to Palestine; he was imprisoned and sentenced to death in Franco's Spain; escaped Occupied France; and, was a member of the Communist party for seven years, later becoming one of its fiercest critics with the publication of ''Darkness at Noon''. Without sentimentality, Scammell gives a full account of Koestler's turbulent private life: his drug use, manic depression, the frenetic womanizing that doomed his three marriages and led to an accusation of rape, and his startling suicide pact with his wife in 1983. Koestler also gives a full account of the author's voluminous writings, making the case that the autobiographies and essays are fit to stand beside ''Darkness at Noon'' as works of lasting literary value. Michael Scammell creates an indelible portrait of this brilliant, unpredictable, and talented writer, once memorably described as 'one third blackguard, one third lunatic, and one third genius'.