Al says that it can be read at any point, and that's really true, but the epilogue has a hint that an unnamed person is Khouri, at a time right before Revelation Space. Chasm City is visited in the other books, but there's nobody in the semi-series that's also in this, so there's no reason to read it in any order, but in fact, I liked reading it after the first three because they describe some equipment and ideas that are just named in this book.
This starts with two narratives that narrow into one: Tanner Mirabel is a security guard/assassin on Sky's Edge (where Khouri is from) and Sky Haussman is the guy who founded Sky's Edge 200 years earlier.
Tanner is working for a man named Cahuella who sells weapons to anybody. Somebody who bought weapons from him killed Reivich's family, and now Reivich is planning to kill Cahuella. Cahuella goes up to the Ultra lighthugger to get some extra body bits and comes back down to ambush Reivich. The Ultras go with the better payer and aid Reivich, and Cahuella and his wife Gitta, who Tanner also loves, are killed.
Tanner sets out to find Reivich, but he's already left the planet, so Tanner follows him in cryosleep. When Tanner awakes with the other "slush" at a nursing habitat above the planet Yellowstone, he has blood coming out of the center of his right palm. This is caused by an indoctrinal virus used by one of Sky's cults. He also starts having dreams of Sky's life -- from his childhood eventually to his arriving on what had been called Journey's End but became Sky's Edge.
Sky is psychotic and loves to hurt people, and Tanner's dreams have episodes that are not known on Sky's Edge or by Sky's followers. When Tanner gets down to Chasm City, it turns out not to be the wonderful city it used to be. The Melding Plague has arrived and strongly separated those with money and those without. Tanner continues to get dreams and then episodes while he's awake of Sky, some of which help him, and is still trying to find Reivich to kill him. He gets involved with several groups of people, all dangerous, and has to figure out how to get what he wants. By the end, things are very different from the start.
I really liked this one -- it comes to a solid finish and the story is very good.