Eternity is one very good novella, intermixed with an okay novella, and a mediocre one. Unfortunately, the mediocre one is the most important.
Roughly 30 years after the events of Eon, the characters are trying to make sense of what comes next.
The good part is Rhita, granddaughter of Patricia Vasquez from Eon, stranded on an alternate Earth dominated by Ptolemaic heirs of Alexander the Great. A gifted scholar, carrying the strange artifacts of her grandmother, Rhita lives in a deft, Greek inspired alternate Earth, and has to negotiate a way to open a gate back to the Way, without understanding the consequences. I loved the glimpses of alternate history, and wished there were more of that.
The okay novella follows Olmy, as he investigates the great secret of the Jart War. It seems that at some point, Hexamon Defense captured a Jart and hit it away in Thistledown. Olmy's last mission is to interrogate the Jart, a combination of diplomacy, cryptography, and mind-to-mind combat. It turns out the Jarts a cybernetic collective, with a goal of archiving every lived experience. They are interesting antagonists, though the military aspect of the series has always been a weak point.
The mediocre novella follows Lanier, now an old man who has refused regenerative medicine, and the political struggle between rebuilding Earth in the aftermath of a nuclear war, and reopening the Way. Pavel Mirsky reappears, an avatar of a godlike intelligence at the end of time, with a dangerous message. The Way must be destroyed for the universe to reach its fulfillment. The politics and cosmology are scattershot, and the meditates about death and the growing distance between Lanier and his wife Karen little more than cliches.