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.

Haimey Dz is a salvage tug operator that gets involved with ancient alien technology, pirates, assorted aliens, and social ethics. She, her shipmate Connla, their AI Singer, and two cats head out to the edge of the Milky Way to check out a potential salvage claim. The first thing they find at the coordinates is a dead Ativahika, a large space going alien species that resembles a seahorse. The Ativahika are presumed to be sentient, although they don't seem to communicate in any obvious way. The ship they are hoping to salvage is of unknown alien manufacture and apparently has artificial gravity, a technology that could make Singer and his small crew a fortune. But the ship also contains a horrible secret that drags Haimey and her friends into a galaxy spanning adventure that will force her to reevaluate everything she thinks she knows about herself.