[1] Approximately six million years in the future, humanity has spread throughout the Milky Way galaxy, which appears devoid of any other organic sentient life.

Large-scale human civilizations almost invariably seem to collapse and disappear within a few millennia (a phenomenon referred to as "turnover"), the limits of sub-lightspeed travel making it too difficult to hold interstellar empires together.

The Lines do not inhabit planets, but instead travel through space, holding reunions after they have performed a "circuit" of the galaxy; something that takes about 200,000 years.

The clones and Abigail travel the Milky Way Galaxy, helping young civilizations, collecting knowledge, and experiencing what the universe has to offer.

After being tricked by Ateshga, Campion and Purslane manage to turn the tables on him and leave his planet with a being he had been keeping captive, a golden robot called Hesperus.

However, before reaching the reunion world, Campion and Purslane encounter an emergency distress signal from Fescue, another Gentian shatterling.

Hesperus, still critically wounded following the rescue of the survivors, is taken to the Neumean "Spirit of the Air", an ancient posthuman machine-intelligence, in the hopes that it will fix him.

Bewildered by this sudden change of events, Purslane delays in acting, not sure if she should trust Hesperus, before deciding to ask the ship to detain and eject the robots in the bridge.

The Commonality (a confederation of the various Lines), horrified and ashamed of this pointless genocide, erased all knowledge of the event from historical records and their own memories.

Hesperus believes that the ambush at the reunion was seeking to destroy this evidence before it could spread, carried out by a shadow Line known as the "House of Suns", tasked with maintaining the conspiracy.

Campion, now the only shatterling still in pursuit, enters the wormhole after them and emerges in the Andromeda Galaxy, a place apparently devoid of all sentient life.

In his search for Purslane and her ship, he travels to a star encased in a huge representation of the Platonic solids, lands on a planet orbiting inside the structure and is greeted by a single, mechanical being, which announces itself to be the last of the First Machines in the Andromeda Galaxy; the others having left (via wormholes) in pursuit of more advanced technology and knowledge.

Lisa Tuttle, reviewing for The Times, called the novel a "thrilling, mind-boggling adventure" with "visionary brilliance" and a "knock-your-socks-off ending".

[3] At SF Signal, one reviewer noted that a "sense of wonder is where this book excels", adding that "Reynolds is playing on a galactic-sized canvas and uses believable science to back up his grand ideas...[t]his yields mind-boggling time scales, where millennia pass by like days".

[4] George Williams, in his review for The Australian, said that "the concepts explored in House of Suns are so far removed from our time, and even from much of the standard fare of science fiction, that parts of the book border on fantasy.