1933 - 1936 Paris

Against the nightmarish background of Nazi Germany, my doubts and misgivings about Russia paled into insignificance. When you march in a crusade, even in a losing crusade, you are not in a mood for reflection. Reflection only set in, with a vengeance, a few years later, when the Russian purges assumed the proportions of mass terror. But that crisis, which would lead to my break with the Party, was still in the future.
In the meantime, Paris was the centre of the international anti-Fascist movement, in which the German Communists in exile played a leading part. In The Invisible Writing I have described in some detail the activities in which I was involved in this period of transition and abortive hopes: the writing of propaganda pamphlets, editing various émigré newspapers, fund-raising for a variety of causes, liaising with French intellectuals, and so on. As most of these jobs were unpaid, and I was still reluctant to become a professional Party bureaucrat or apparatchik, I secured my financial independence for a while by writing, under the pen-name A. Costler, a popular-science book on sex-one of the first of its kind, I believe, long before the genre became a commercialised industry. (Ironically, it is the only book I wrote that was received with unanimous praise by the critics). I was paid no royalties, but the modest flat sum I got .from the publishers enabled me to embark on an ambitious historical novel on the slave revolt in the first century BC in Rome - The Gladiators - which eventually became the first of a trilogy of novels on the ethics of revolution.
I was immersed in writing The Gladiators when the Spanish Civil War exploded and made the horrors of Nazi Germany and Soviet Russia temporarily fade into the background.

The books published under the name of Dr. Costler were for Koestler an expedient to earn himself a living and allow him to keep working on his other activities that generally brought him very little or no money at all.