Chasm City is a science fiction book by author Alastair Reynolds. It's set in the Revelation Space universe.

Chasm City is framed and largely written in the voice of Tanner Mirabel, a rather dull security expert who has come to Chasm City to avenge the death of his former client at the hands of a "postmortal" named Argent Reivich. But alternating with this story, we get another story, the story of Sky Haussman, now seen as a political criminal, but at one time regarded as a colonizing hero. As Mirabel enters Chasm City and burrows deeper and deeper into the mystery of the City, the riches and the plague, Haussman's life unravels before the reader's eyes.

Tanner Mirabel finds in the end that he is actually his client, Cahuella, who is actually Sky Haussman.