George Simling has grown up in the city-state of Illyria, an enclave of logic and reason founded as a refuge from the Reaction, a wave of religious fundamentalism that swept away the nations of the twenty-first century. Yet to George, Illyria's militant rationalism is as stifling as the faith-based superstition that dominates the world outside its walls.

For George has fallen in love with Lucy. A prostitute. A robot. She might be a machine, but the semblance of life is perfect. To the city authorities, robot sentience is a malfunction, curable by erasing and resetting silicon minds. But George knows that Lucy is something more.

His only alternative is to flee Illyria, taking Lucy deep into the religious Outlands where she must pass as human because robots are seen as mockeries of God, burned at the stake, dismembered, crucified. Their odyssey leads them through betrayal, war and madness, ending only at the monastery of the Holy Machine...