It is the tale of young Severian, an apprentice in the Guild of Torturers on the world called Urth, exiled for committing the ultimate sin of his profession - showing mercy toward his victim - and follows his subsequent journey out of his home city of Nessus.

    The age of star formation is long past. Yet there is life here, feeding off the energies of the stellar remnants, and there is mind, a tremendous galaxy-spanning intelligence each of whose thoughts lasts a hundred thousand years. And this mind cradles memories of a long-gone age when a more compact universe was full of light... The 27th century: Proxima Centauri, an undistinguished red dwarf star, is the nearest star to our sun. How would it be to live on such a world?