Short story/novella by Samuel R. Delany about a young man, Comet Jo, who is sent to deliver an important message to Empire Star. Jo, an interstellar country bumpkin, must leave his home-world Rhys to do this. Along the way, he meets Oscar, a mysterious woman called Ni and an enslaved race of builders called the Lll as he evolves from a "simplex" to "multiplex" being.
An attentive reader will note that Empire Star was written by a character in Babel-17.