"Hailed as 'one of the most inventive writers that science fiction has ever produced' (SF Site), Stephen Baxter builds on the massive success of Proxima with a career-defining novel of big ideas.... On the planet of Per Ardua, alien artifacts were discovered--hatches that allowed humans to step across light-years of space as if they were stepping into another room. But this newfound freedom has consequences.... As humanity discovers the real nature...