Reynolds (The Prefect) returns to the universe of his 2005 novella Thousandth Night in this sprawling novel of intergalactic intrigue. It is 6.4 million years in the future and humanity has spread throughout the Milky Way. Some cultures have established transient empires across space; others, the Lines, have used relativistic travel to colonize deep time. Clone-siblings Campion and Purslane are delayed on their way to a Gentian Line reunion, a coincidence that saves them from a massacre. Allied with potentially hostile Machine People and an enigmatic post-human god called the Spirit, armed only with fragmentary records and hints that Campion’s research provoked the mysterious House of Suns, the Gentian survivors struggle to find and stop their enemies before the genocide can be completed. Intriguing ideas and competent characterization make this a fine example of grand-scale relativistic space opera.