The Trial by Franz Kafka
When people use the adjective 'Kafkaesque', it is The Trial they have in mind - the nightmarish world of Joseph K., where the rules are hidden from even the highest officials, and any help there may be comes from unexpected sources.
K. is never told what he is on trial for, and when he says he is innocent, he is immediately asked 'innocent of what?' Is he perhaps on trial for his innocence? Could he have freed himself from the proceedings by confessing his guilt as a human being? Has the trial been set up because he is incapable of admitting his guilt, and hence his humanity? The Trial is a chilling and at the same time blackly amusing tale that maintains, to the very end, a constant, relentless atmosphere of disorientation and quirkiness. Superficially the subject-matter is bureaucracy, but the story's great strength is its description of the effect on the life and mind of Josef K. It is in the last resort a description of the absurdity of 'normal' human nature.