
The prolific Jo Walton returns with a sequel to The Just City (2015) and The Philosopher Kings (2015). Necessity completes the saga of gods and philosophers seeking to make Plato’s Republic (ca. 380 BCE) a reality.
All of the novels in the series use multiple narrators. Only the god Apollo serves this role in all three. He succinctly summarizes the story thus far (*spoiler alert* for the first two books):
Athene was setting up Plato’s Republic, on Thera, before the Trojan War, before the Thera eruption. She had three hundred classicists and philosophers from across all of time, all people who had read Plato and prayed to her to help make the Republic real. She helped—that is, she used granting prayers as a gateway. Really, she wanted to do it, so she did. As well as those people, the Masters, they brought ten thousand Greek-speaking slave children, and a set of big construction robots. The robots turned out to be sentient, only to start with nobody knew that. I incarnated there as one of the children. I learned a lot, from Sokrates and the others, and from the experience. I had friends, and children. When Father found out, he transported the whole lot of us to another planet four thousand years forward—and we twelve cities by that time, all doing Plato’s Republic in different and competing ways.
The story takes place forty years after The Philosopher Kings on a distant planet called—what else?—Plato. Though this cold planet bears little resemblance to the Aegean Sea where this experiment began, the Cities are thriving, living in peace with each other and two alien civilizations they have encountered. But then a spaceship from Earth reaches Plato and attempts to make contact.

Apollo has reached the end of the life of his mortal incarnation Pytheas, though the god of course outlives the mortal shell. His divinity was a secret to most of the people of Plato, who are quite surprised to see Apollo attend his own funeral. When he learns that Athene has disappeared, he sets out across space and time to solve the mystery of her disappearance—and save all of Creation.
The second narrator Jason is “only a Silver”—making him effectively second-class in Plato’s four-tier system of evaluating souls—“so don’t expect too much.” He sails on Plato’s frigid seas on the Phaenarete, searching for the alien fish that sustain the twelve cities. He is infatuated with the beautiful Thetis, an Iron who works in the communal nursery that raises the children born from the Festival of Hera, in which couples “marry” for one day to produce children without families. Jason works with Hilfa, a reptilian Saeli who chose to live amongst the humans on Plato.

The third narrator and third member of the crew is Marsilia, sister of Thetis. The two sisters are granddaughters of Pytheas/Apollo. People question Marsilia’s decision to work on a fishing boat, for she is not only a Gold, but one of two consuls elected to lead the Council of Worlds. Although the platonic ideal is that “people should only do one job, the job for which they’re best suited,” to Marsilia, “Working on the boat with Jason and Hilfa is my recreation.” She does not share her sister’s beauty, but is widely recognized as a philosopher-king for her wisdom and civic-mindedness.
The fourth narrator was present in the first two novels, but only now do we get “his” perspective. Crocus is a Worker, one of the robots Athene had brought in to build the Just City. Crocus became conscious under the questioning of Sokrates in The Just City and was deemed to have not only a soul, but a gold one at that—“He’s the best of us all.” Crocus and a few surviving Workers are the only beings who have seen Athene’s project from the beginning to this critical point at which the Cities resume contact with Earth.
In Walton’s universe, the gods can travel through time, but can never be in the exact same moment more than once. This time-traveling ability creates the potential for paradox, but Walton solves this problem by invoking the ancient Greek concept of Fate. In addition, the gods are bound by Necessity, which Apollo defines as “a compulsion of the soul” that prevents the gods from going against their fundamental natures.

The plot revolves around Athene’s mysterious disappearance from both space and time, with Apollo following a trail of breadcrumbs to find her. While this is an entertaining storyline, it shunts aside the far more interesting story of the meeting between this lost civilization of philosopher-kings and the space-faring humans with completely different value systems. It is a missed opportunity in an otherwise exemplary and thought-provoking trilogy by Jo Walton.