The story is an autobiographical tale told by a Roman soldier, Marcus Flaminius Rufus. He is determined flee from the deserted battlefield to find the city of immortal and a river which contains the power of immortality.

Weeks later he finds the river and the City of the Immortals, where live a bunch of dwell-living men. The city is an immense labyrinth with dead-end passages, inverted stairways, and many chaotic architectural structures. He eventually escapes the city and finds one dwell-living man waiting outside; he names him Argos (after the dog of Odysseus), and decides to teach him language. Soon after, though, Argos reveals that he is Homer, and
that the dwell-livings are the Immortals.

Rufus spends centuries living with the Immortals, mostly immersed in thought, until he knows the existence of a river with the powers to "take away" immortality. He then travels around the world and finally finds the river that takes his live away.