At a time when artificial intelligence (AI) seems like both a menace and a boon, it’s tempting to dismiss it as something not yet fully formed and therefore ignorable (why can’t picture-generators get fingers right?). Erika Swyler’s gritty, expansive new novel, We Lived on the Horizon, asks intriguing questions about how the wholesale integration of AI into our lives will affect and change humanity regardless of our feelings toward it.

The walled city of Bulwark — a survivor in the post-apocalyptic world — is overseen by a sprawling AI network called Parallax, which tracks, evaluates, and ranks the personal sacrifices of individual citizens, effectively imposing a rigid class system:

“Better is a concept of degrees leading to the dissection of minutiae. Parallax exists because humans are not skilled at differentiating between what is worth changing and what is best forgotten.”

Parallax also makes decisions purportedly in the city’s best interest — an approach that can charitably be described as “for the greater good,” or uncharitably as cutthroat — but unrest is nonetheless growing among the citizenry. While the have-nots must often resort to erasing their life debt and gaining status by making extreme personal sacrifices, others — beneficiaries of wealth “earned” via their ancestors’ long-ago selfless acts — rest comfortably atop laurels passed down through the generations.

At the apex of the ranks are the city’s elite “Sainted”: descendants of the original families who gave everything to help build and expand Bulwark. When Saint Lucius Ohno is murdered and Parallax mysteriously overwrites the suspicious circumstances surrounding the killing (thereby keeping it from the public), Saint Enita Malovis and her companion, Saint Helen Vinter, take notice.

As Helen investigates Ohno’s death, Enita grapples with a different quandary. Long known to the city’s poor and desperate as a surgeon who grows organic limbs and digits to replace, for free, mangled body parts, Enita — nearing the end of her career — is presented with Neren, a severely injured young woman in dire circumstances, whom she quickly treats.

Only too late does Enita discover that Neren is a Body Martyr — someone who donates parts of their body to restore others to health — a crucial designation dictating that Neren’s body must never be altered, as Enita has just done. That generous act all but breaks Neren’s spirit:

“For two full weeks Neren refused to speak. She saw no point in bothering, not when her body no longer felt like her own, when the only words she had were you should have let me die. She didn’t want to give [her partner] the chance to respond, to prove once again that she’d never understood Neren at all. Beneath the anger, the betrayal, was solitude’s heartbreak. Her partner had been no such thing.”

Assisting in Enita’s endeavors is Nix, an AI being created by Enita herself to absorb her medical knowledge and one day continue her healing work. Although Neren is at first wary of Nix, the Body Martyr comes to believe Nix understands her in a way others cannot, even as Nix themself is changing in ways they don’t understand:

“There was something that might be fascination in the way Neren looked at Nix, even perhaps a little of the awe art could provoke. Enita was unable to view Nix without seeing everything they’d been before their current form, every error and all the perfection. She could only view them with the eyes of an artist and a mother, and sometimes, ever so rarely, as though she was their child.”

While Enita, Neren, Helen, and Nix are discovering new facets of themselves and each other, the city continues to disintegrate under the weight of its people’s increasing agitation. As Helen says to Nix, “Societies are meant to change, and Bulwark has been stagnant for too long.”

In fact, as their investigation progresses, the four collaborators come to believe Parallax itself is playing a role in Bulwark’s downfall, although what that role is, they can’t yet discern. “People are good at making systems,” someone who works closely with Parallax tells them. “We’re not so good at understanding how to care for other people. Parallax knows this. They know the time for them is changing.”

The seemingly disparate events that tie the three women and the AI Nix together will eventually require them to make decisions fraught with pain, love, fear, and desire. Through it all, Swyler’s slow burn of a story continues to ask challenging, unanswerable questions about what it means to be human and what it means to evolve.

Mariko Hewer is a freelance editor and writer as well as a nursery-school teacher. She is passionate about good books, good food, and good company. Find her occasional insights of varying quality on Twitter at @hapahaiku.