Children of Memory by Adrian Tchailkovsky

The modern classic of space opera that began with Children of Time continues in this extraordinary novel of humanity's battle for survival on a terraformed planet.

Earth failed. In a desperate bid to escape, the spaceship Enkidu and its captain, Heorest Holt, carried its precious human cargo to a potential new paradise. Generations later, this fragile colony has managed to survive, eking out a hardy existence. Yet life is tough, and much technological knowledge has been lost.

Then strangers appear. They possess unparalleled knowledge and thrilling technology – and they've arrived from another world to help humanity’s colonies. But not all is as it seems, and the price of the strangers' help may be the colony itself.