"Darkness at Noon" is an expose of Stalinism. The protagonist (Rubashov) is a devoted communist who fought in the Russian Revolution, but has fallen afoul of the current regime. He is imprisoned, questioned, forced to sign confessions, and executed.
The novel feels a little dated, to me. Everyone now knows the evils of Stalinism. Nonetheless, Rubashov is an interesting character -- an idealist who is conflicted about loyalty to the "Party", or loyalty to the goal of world revolution. Apparently, Stalin (known as "#1" in the novel) wanted to hunker down and abandon world revolution, and had anyone whose opinion differed shot.
Rubashov is an interesting chap, and when his questioners want him to sign a document admitting that he tried to assassinate Stalin (a crime of which he was not guilty) he is willing to sign, but objects to the stupidity of the plot to which he is confessing. He doesn't want to look like a fool.
The novel is a short, easy, and dramatic read.