Some of the characters from Ancestral Night make cameo appearances, but Machine isn't really a sequel. The story follows Dr. Jens, who enjoys her job on an interstellar ambulance crew dealing with a wide variety of medical emergencies. Some of these involve humans but there are so many species here that every call for help is a new challenge. The AI that runs the ship decides to take one last call before heading to the central system, the equivalent of jury duty in the US, and they find two ships locked together with the biological beings unconscious and the ship AIs confused and acting strangely. The take all of them back to Central Hospital and soon all sorts of things start happening in the usually boring station. Someone actually attacks them, the AIs forget things, and there are power failures for no reason, which could be deadly for the patients. But what Dr. Jens finds strangest of all is that there is a ward restricted to only a few personnel and no one knows who the patients are or what treatment they are receiving. Somehow it connects back to those two ships and the crippled AI, so Dr. Jens is determined to find answers.

The Raven God's vessel, a possessed raven, is dead. According to the agreement between the people of Vastai and the Raven God, their ruler, the Raven's Lease, must now sacrifice himself to empower the Raven while it incubates in a new egg. The Lease's Heir, his son Mawat, returns from his military post at the border to find that his father has vanished without being sacrificed and his uncle claims to be the new Lease. It's supposed to be impossible to usurp the Lease so Mawat is certain something is very rotten in Vastai. Another god, Strength and Patience of the Hills, tells the story of Mawat's revenge intermixed with its own history to Mawat's faithful retainer Eolo. Only Eolo senses the doom descending on Vastai.