The God Engines is a short SF book by John Scalzi. It’s set in a distant future where ships adhering to the Mighty Lord ply the stars fighting battles and the like – a very Warhammer 40k-ish bleak setting. What makes any given ship (and the story) go is the defeated god chained up in its lower decks. These gods (one per ship) are the defiled unworthy competitors to the One God who defeated them in ages long past, and the only thing letting people survive in the coldness of space and travel across the galaxy.
The story is about a captain with very good judgment and the mission he is called upon to perform. He has a stalwart first officer and a lousy priest on board. I won’t spoil the story but the book is a very interesting examination of the nature of faith in a SF context. It’s short, but does its job well.
I think having read this just before seeing Prometheus might have shifted my expectations for the movie a bit, through no fault of either Scalzi or Scott. I thought they would be dealing with similar questions but one treated them thoughtfully while the other posed like it did.