Sergei Tretyakov is one of those artists and intellectuals from the first half of the twentieth century whose name is known, but whose achievements are barely recognized. He seems curiously elusive. Who exactly was he? What did he do? A victim of Stalin's Great Terror, declared an 'enemy of the people', his works were 'disappeared' and his name forbidden to be mentioned. But he was at the very heart of avant-garde modernism. He collaborated...