"Un-Man" was nominated for a retro-Hugo for best novella of 1953 at the 2004 World Science Fiction Convention.
Robert Naysmith is a member of the United Nations Inspectorate, an international police force that neutralizes threats to world peace. He is also a member of the Rostomily Brotherhood, a secret order within the Inspectorate made up of men cloned from Stefan Rostomily, a member of the French resistance during World War III.
Naysmith is ordered to carry on the assignment of Martin Donner, another member of the Brotherhood who was killed while investigating an anti-UN conspiracy. Atypically for a Brother, Donner had a wife and child, and Naysmith's first task is to impersonate Donner long enough to persuade his family to go into hiding with him. Naysmith leaves Donner's wife and son in an isolated cabin in the Canadian Rockies. He then kidnaps and drugs a member of the conspiracy, learning that he has been assigned to assassinate Barney Rosenberg, a Martian colonist who is returning to Earth to retire. Naysmith teams up with a Finnish Brother named Juho Lampi to rescue Rosenberg, and learns that he was a close friend of the original Rostomily.
After leaving Rosenberg with the Donners, Naysmith and his partner arrange to be captured by the conspiracy. They are brought to the secret sea base of Arnold Besser, UN Minister of International Finance and the leader of the conspiracy. They find themselves joined by two more captive Brothers, along with Besser himself. Before Besser can begin torturing Naysmith and the others, the secret base is attacked by UN police, and Besser's bodyguard (actually another Brother, surgically altered to look like Besser's bodyguard) kills Besser and frees the others. Following the raid, the information found in Besser's secret base allows the UN to roll up the conspiracy. Donner's wife tracks down Naysmith and asks him to marry her.
The United Nations, reconstituted in Rio de Janeiro after the destruction of New York City in the war, is slowly being transformed into a federal world government. The nations of the world are kept under surveillance, and under armed guard, by UN-controlled bases on the Moon. The UN routinely intervenes to head off wars; sometimes openly through the use of armed force, and less openly through assassination to prevent resurgent nationalism.
Nationalism, including American nationalism, is depicted as the great enemy of mankind in "Un-Man". The leadership of a nationalist American political party is a hotbed of psychotic individuals, while the agents of the UN are dedicated to the preservation of sanity. The nationalists of various countries are mentioned as involved in a kind of alliance of convenience, aimed at getting rid of the restrictions imposed by the UN (whereupon they would be free to fight each other)
The story is unique among Anderson's writings, where usually the protagonist's opponents are given the honour of their own convictions and the reader is given at least glimpse of their point of view and motivations. Conversely, in the present story the villains are entirely evil psychotics, with not a single redeeming feature, and the reader is made to share the protagonists' complete and visceral loathing and hatred of them.
It should be noted that the time when the story was written, making the fictional "Americanist Party" into such utter villains, was the peak time of the demagogic "Witch Hunt" carried out by Senator Joseph McCarthy and the House Un-American Activities Committee. "Un-Man" might indeed be considered a parody on "Un-American". (By his own later testimony, Anderson was "a flaming liberal" when he wrote this story).
In "The Sensitive Man" Anderson repeated many of the themes of the present story, but in a more subtle and nuanced way and with his more usual kind of villain - i.e. one who is not completely black, who is given some sympathetic traits, but who is nevertheless shown as acting wrongly and needing to be opposed and defeated.