Darkness at Noon is a fictionalized treatment of the purge trials that took place In the Soviet Union in the late 1930's. Stalin's aim was basically to eliminate the Bolshevik old guard, people like Trotsky and Bukharin who had been instrumental in making the 1917 coup a success but whom Stalin no longer trusted. Huge numbers of these men were thrown in jail, forced to sign false confessions that they had betrayed the Revolution, and shot. (Trotsky himself escaped the Soviet Union but was assassinated in Mexico by a probable agent of Stalin.) Koestler presents the fictitious character Rubashov as a kind of composite of the old Bolsheviks. He is arrested in the night and thrown in prison. Though this is obviously taking place in the Soviet Union, Koestler never actually names the country, and the leader, Stalin himself, is referred to simply as "Number One."
From the moment he's placed in isolation in his cell, Rubashov knows he is going to be shot. He expects to be beaten and tortured first, but this does not happen. Instead he's interrogated and worn down psychologically. His memory and perception of his past actions become distorted, and, though he never did betray Number One and the Communist cause, he reaches a point where he does not really know what he did or what his motives were. He confesses his "crimes," and at the novel's close is his execution in the prison cellars with a bullet to the back of the head.
Koestler's account tells us that Stalinism and its brand of totalitarian control were essentially no different from a Fascist regime. This may not come as anything startling to us, but Koestler himself had been a Communist Party member, and at the time he wrote the book, left-wing people in general were either in denial about the cruelty of Stalin's regime, or simply did not know about what was taking place internally in the Soviet Union. In Stalinist Russia, any remnant of the rule of law that might have remained after the 1917 Revolution had disappeared, replaced by the paranoid authoritarianism of Stalin himself. Rubashov's fate demonstrates the most far-reaching feature of the totalitarian state: mind control. It is not simply that citizens are forbidden to question the regime: the effect of a total dictatorship is to destroy the concept of objective reality. Truth becomes not what is objectively observed or remembered, but instead, whatever "Number One," the leader, declares it to be. Rubashov is manipulated into stating, and even believing, not what he knew as truth, but what the regime tells him is true. It is a mental, as well as physical, enslavement of the civilian. George Orwell, who was heavily influenced by Koestler, depicts a dystopia in 1984 that is a projection of this Stalinist mind control into a nightmare future.
Rubashov's story is complicated by the early realization, before he is interrogated, that his actual behavior in the service of the Party, while it may have been loyal, has been ruthless and cruel. He recalls in detail episodes in which he acted against his own principles in getting other Party members arrested and killed for their own supposed transgressions. His case, in his being imprisoned and finally executed, illustrates the adage that whatever goes around, comes around. It also shows that in a totalitarian regime like Stalin's, even well-intentioned men, as Rubashov originally was, end up betraying their own values in the service of the despotic government.