Michael Scammell is to be congratulated for this magnificent biography. If you want to find out how brilliant, how selfish, how brave, how childishly promiscuous and how influential Arthur Koestler was, this is the book. If you want to know where Koestler was and when, and in the company of which woman or women, at various points during his turbulent career, you could not ask for a more serious, carefully researched and riveting text. The subtitle, stressing Koestler’s importance, is well judged too. He did more than anyone, except perhaps Solzhenitsyn later, to disenchant the world with the communist fantasy.…