Helix Wars by Eric Brown. The sequel to Helix and a very enjoyable sci-fi adventure.
"The Helix: a vast spiral of ten thousand worlds turning around its sun. Aeons ago, the enigmatic Builders constructed the Helix as a refuge for alien races on the verge of extinction.
Two hundred years ago, humankind came to the Helix aboard a great colony ship, and the Builders conferred on them the mantle of peacekeepers. For that long, peace has reigned on the Helix. But when shuttle pilot Jeff Ellis crash-lands on the world of Phandra, he interrupts a barbarous invasion from the neighbouring Sporelli - who scheme to track down and exterminate Ellis before he can return to New Earth and inform the peacekeepers."