The Case of Comrade Tulayev by Victor Serge (1949)

Ok, I confess. I have a macabre penchant for gulag fiction, and this is my favourite of the lot. While Koestler & Solzhenitsyn graphically portray interrogation and exile respectively, Serge takes a panoramic approach showing how a Stalinist purge rippled out from a random incident to ensnare old heroes and young zealots alike. And he ought to know - having spent years in a Russian prison in the 1930s. This is a masterfully constructed tale written in an immensely readable style, but it is the unique window into the remorseless machinery of a totalitarian state and its justifications that make this book essential cautionary reading.