I've studied 'Darkness at Noon' closely, and while it's fiction, Koestler clearly drew from real Stalinist purges. The protagonist Rubashov's interrogation mirrors actual show trials where Bolsheviks confessed to absurd crimes. The psychological manipulation techniques—sleep deprivation, forced self-criticism—match NKVD methods documented in archives. What chills me is how Koestler, a former Communist, captured the internal logic of totalitarianism. The novel's setting resembles 1938 Moscow, but it's not about one specific trial. It synthesizes patterns from multiple victims like Bukharin and Zinoviev. The brilliance lies in showing how revolutionaries become prisoners of their own system, a universal theme beyond just Soviet history.