The story is narrated in the first person by the unnamed magistrate of a small colonial town that exists as the territorial frontier of "the Empire". The Magistrate's rather peaceful existence comes to an end with the Empire's declaration of a state of emergency and with the deployment of the Third Bureau—special forces of the Empire—due to rumours that the area's indigenous people, called "barbarians" by the colonists, might be preparing to attack the town. Consequently, the Third Bureau conducts an expedition into the land beyond the frontier. Led by a sinister Colonel Joll, the Third Bureau captures a number of barbarians, brings them back to town, tortures them, kills some of them, and leaves for the capital in order to prepare a larger campaign.
In the meantime, the Magistrate begins to question the legitimacy of imperialism and personally nurses a barbarian girl who was left crippled and partly blinded by the Third Bureau's torturers. The Magistrate has an intimate yet uncertain relationship with the girl. Eventually, he decides to take her back to her people. After a life-threatening trip through the barren land, during which they have sex, he succeeds in returning her—finally asking, to no avail, if she will stay with him—and returns to his own town. The Third Bureau soldiers have reappeared there and now arrest the Magistrate for having deserted his post and consorting with "the enemy". Without much possibility of a trial during such emergency circumstances, the Magistrate remains in a locked cellar for an indefinite period, experiencing for the first time a near-complete lack of basic freedoms. He finally acquires a key that allows him to leave the makeshift jail, but finds that he has no place to escape to and only spends his time outside the jail scavenging for scraps of food.
Later, Colonel Joll triumphantly returns from the wilderness with several barbarian captives and makes a public spectacle of their torture. Although the crowd is encouraged to participate in their beatings, the Magistrate bursts onto the scene to stop it, but is subdued. Taking the Magistrate, a group of soldiers hangs him up by his arms, culminating his understanding of imperialistic violence in a personal experience of torture. With the Magistrate's spirit clearly crushed, the soldiers mockingly let him roam freely through the town, knowing he has nowhere to go and no longer poses a threat to their mission. The soldiers, however, begin to flee the town as winter approaches and their campaign against the barbarians collapses. The Magistrate tries to confront Joll on his final return from the wild, but the colonel refuses to speak to him, hastily abandoning the town with the last of the soldiers. The predominating belief in the town is that the barbarians intend to invade soon, and although the soldiers and many civilians have now departed, the Magistrate helps encourage the remaining townspeople to continue their lives and to prepare for the winter. There is no sign of the barbarians by the time the season's first snow falls on the town.