Empyrion by Stephen Lawhead

Traveler, debt-dodger, itinerant critic, and writer of history books nobody buys, Orion Treet is astonished when he's invited to accompany a top-secret mission to observe and document an extraterrestrial colony on a newly discovered planet. But when Treet and his companions reach the paradise planet they have been promised, they find themselves enmeshed in an ancient and deadly conflict between two highly evolved civilizations. Can the free and perfect world of Fierra escape annihilation? Treet, with a handful of rebels, stands alone against the evil might of Dome, as events move inexorably towards a world-shaking climax.