Greg Bear

In the wake of apparent self-destruction of the Forerunner empire, two humans--Chakas and Riser--are like flotsam washed up on very strange shores indeed. Captured by the Master Builder, misplaced during a furious battle in space, they now find themselves on an inverted world where horizons rise into the sky, and where humans of all kinds are trapped in a perilous cycle of horror and neglect. For they have become both research animals and strategic...