Cosmonaut Keep swaps between two timelines whose characters share the ultimate goal of interstellar travel. In an uncertain future on the far world of Mingulay, human colonists live in the title's ancient, alien-built Keep--coexisting with reptilian "saurs," trading with visiting ships piloted by krakens, and hiding their laborious "Great Work" of developing human-guided navigation between the stars.

Meanwhile, alternate chapters present a mid-21st-century Earth whose EU is (to America's horror) Russian-dominated with a big red star in the middle of its flag. Rumors of alien contact abound, and computer whiz kid Matt Cairns finds himself carrying a data disk of unknown origin that offers antigravity and a space drive.

Clearly, the later storyline's Gregor Cairns is Matt's descendant. There are ingenious connections and surprises, with witty resonances between their wild careers, their travels, and their bumpy love lives. The foreground action adventure points to a bigger picture and a master plan known only to the godlike hive-minds who built the "Second Sphere" of interstellar culture, and who regard traditional SF dreams of unlimited human expansion through space as precisely equivalent to floods of e-mail spam polluting the tranquil galactic net.

Cosmonaut Keep opens MacLeod's new SF sequence, Engines of Light. It's highly entertaining and intelligent, promising more good things to come. --David Langford