4 ideas
An unnamed man reports to the Third Pentagon, a military complex sealed inside a mountain, and receives a mission that is never actually explained. He is passed from office to office, handed his instructions in a sealed envelope that goes missing, meets officers and priests who may be spies or provocateurs, and eventually finds that the mission itself may be a test of his loyalty. Increasingly desperate, he ends up in a bathroom contemplating suicide.
If an institution assumes that any message might be a code, then every message ends up read as a possible code, including innocent words, gestures, and silences. Because a code can hide another code beneath it, interpretation never reaches a floor where it can stop. Meaning collapses, since nothing can ever be confirmed as meaning only what it appears to say.
In a system where anyone could be a double agent, loyal behavior and a skilled traitor's cover look exactly the same, so no act can prove loyalty. Every member therefore has to perform suspicion and hide their own intentions. That makes each of them behave just like the enemy agents the system fears. A counterintelligence apparatus pushed to its limit ends up producing the very betrayal it was built to catch.
The book treats a bureaucracy as a machine that makes documents about other documents, with its own reproduction as its real product rather than any outside purpose. Seen this way, a missing mission is not an error. An institution cut off from the world it once served keeps processing its own symbols with no goal behind them.