The author of Darkness at Noon, Arthur Koestler, actually was a communist who sympathized with the Soviet revolution and went to live and work there for years, saw firsthand the brutality of Stalin's regime during the Great Terror of the 1930s, where millions of Russians, Belorussians, Ukrainians and others were starved to death or shot. Millions more were arrested.
Koestler's story lets us into the raging paranoia that was Stalin's regime. Rubashov, the main character, is himself a part of the revolution, but under Stalin the revolution is turning on its own. Rubashov follows the path of millions of others killed by Stalin's government: public denunciation, arrest, lengthy interrogation, and execution.
The novel comes across just like Koestler intended, as a blistering condemnation of Soviet totalitarianism. After his time in the USSR, Koestler resigned from the communist party and published Darkness at Noon.
An interesting sidenote: In the dramatic version of this book, Rubashov says, " Dearth is no mystery to us -- it's the natural conclusion to political divergencies."