Destry is a top network analyst with the Environmental Rescue Team, an ancient organization devoted to preventing ecosystem collapse. On the planet Sask-E, her mission is to terraform an Earthlike world, with the help of her taciturn moose, Whistle. But then she discovers a city that isn't supposed to exist, hidden inside a massive volcano. Torn between loyalty to the ERT and the truth of the planet's history, Destry makes a decision that echoes down the generations.

Centuries later, Destry's protege, Misha, is building a planetwide transit system when his worldview is turned upside-down by Sulfur, a brilliant engineer from the volcano city. Together, they uncover a dark secret about the real estate company that's buying up huge swaths of the planet―a secret that could destroy the lives of everyone who isn't Homo sapiens. Working with a team of robots, naked mole rats, and a very angry cyborg cow, they quietly sow seeds of subversion. But when they're threatened with violent diaspora, Misha and Sulfur's very unusual child faces a stark choice: deploy a planet-altering weapon, or watch their people lose everything they've built on Sask-E.