After the events of the first three books — the discovery of the alien protomolecule, the war it nearly triggered across the Sol system, and the opening of the great alien Ring and its thousand gates to a thousand new solar systems — humanity now stands at the threshold of an unimaginable frontier. The probes have gone through the gates and found sun after sun, world after world, all of them empty; whatever built the protomolecule and fired it at Earth in the deep past is not answering, and no gods have come streaming through. So humanity does what humanity does: since the builders aren't home, can we have their stuff? On Mars, the Ganymede-massacre survivor and Marine veteran Bobbie Draper rides the tube to a family dinner and coldly shames a man falsely begging as a veteran, the old rage never far off. She works veteran's outreach on a homeworld that is quietly emptying out — fewer people in the tube stations, university enrollment falling — as the century-long dream of terraforming Mars loses its young to the lure of ready-made new worlds. At dinner her brother and her nephew David argue that very tension, Mars versus the gates, until a red-bannered newsfeed cuts in: TRAGEDY ON NEW TERRA. Somewhere out past the gates, on the first world humans have tried to settle, something has gone catastrophically wrong — and Bobbie, and the reader, are left staring at the flames.