The explosive final volume in Ken MacLeod's far-future trilogy. Nova Babylonia is in decline. The expected alien invaders never came and the Regime has fallen. Into this corrupt city arrives an outsider whose purpose is ambiguous. But businessman or spy, he is not the only visitor.Engine City completes Ken MacLeod's "Engines of Light" trio of sophisticated, politically astute space operas. Previous volumes were Cosmonaut Keep and Dark Light.

MacLeod has lots of fun with UFO conspiracy theories, since here the saurian-descended "Alien Greys" with their antigravity saucers actually exist. So do hairy Bigfoot-like primates, sea-dwelling selkie folk, and other legends. Planetary fossil records are a misleading mess, thanks to tampering by the "gods".

These gods are hive-mind intellects, vast, cool and irritable, occupying comets and asteroids. They have long been transplanting intelligent species across space, and playing them off against one another, just to keep the noise down--the dreadful racket of radio broadcasts and space exploration. "Their first and last commandment is: do not disturb us."

The mixture of human and other races dumped in the Second Sphere, a far-off galactic region, is up to potentially disturbing activities: an accelerating growth of technology and interstellar trade. Are rumours of octopod alien "Multipliers" mere disinformation, or are these the Gods'-appointed nemesis for the human-led Bright Star Cultures and their commercial empire? Some long-lived cosmonauts, surviving from book one, hope for peaceful diplomatic relations. One, an unreconstructed Russian veteran, urges a massive arms programme on the world of Nova Terra. Everyone, but everyone, is in for surprises.

The twisty narrative has many cheery asides, such as the naming of a flotilla of human-built UFOs: "Matt's suggested names (Rectal Probe, Up Yours, Probably Venus, Strange Light, No Defence Significance) were all rejected..." Or a saurian's patient explanation that antigravity was useless for building their equivalent of the Pyramids, which required enormous ramps of close-packed earth, miles of rope, and tens of thousands of workers: "But when you tell people that, they don't believe you."

Towards the finale on Nova Terra, events are complicated by heavy weaponry, alien symbiosis, a programme of "guerrilla ontology" featuring literal "Men in Black" and devastating intervention by one of the gods. For excellent self-defensive reasons, the Bright Star Cultures class the killing of Gods (theicide) as a heinous crime. The provocation, however, is great...

A highly enjoyable conclusion to a fizzy, fast-moving but persistently intelligent trilogy. --David Langford

Genre: Science Fiction