This second part of Baxter's spectacular hard-science trilogy has nothing in common with Manifold: Time (2000) except the protagonist, astronaut Reid Malenfant. In 2020, Malenfant, forced into retirement following the collapse of the US space program, yet still convinced that humanity must expand into space, spends his time on the speech circuit and wondering why no alien civilizations have been detected, when theoretically there should be many spreading through the galaxy. Then researcher Nemoto detects intruders in the asteroid belt. Engaged in industrial activity, the multi-limbed, robotlike “Gaijin” seem little interested in humanity. Reid and Nemoto cobble together a ship, so that Malenfant can go find the Gaijin star gate. When Malenfant enters, he ends up at Alpha Centauri and runs out of air. The Gaijin save him, begin to communicate, and send him farther and farther afield. Meanwhile, back in the solar system, the Gaijin begin to trade and exchange ideas with humanity. Nemoto accumulates evidence that numerous bodies were modified in the remote past by now-vanished aliens. The Gaijin, indeed, know that new civilizations constantly appear, spread rapidly, then always collapse before maturing. More aliens approach the solar system: these Crackers cause stars to go nova, for reasons unknown; the Gaijin prepare defenses against them. What causes civilizations to collapse every time? Why should the Gaijin bother to defend the solar system, and why are they so interested in Reid Malenfant?
Forget such conventional novelistic virtues as characters, linear plotting, or continuous narrative; instead, Baxter offers challenging puzzles and mind-boggling extrapolations in a sweeping yarn that explodes with ideas.