After her rollicking standalone Dual Memory, Sue Burke returns to her Semiosis series and the world of Pax in Usurpation, which combines the thrill of M. Night Shyamalan's The Happening with the eco-empowerment of VanderMeer's Dead Astronauts.Stevland, the dominant sentient lifeform of Pax, has clandestinely sent some of its progeny to Earth. To explore, to spread, to report back.Since their germination, Earth has been a powder keg. Human rebellion, robot uprisings, and global pandemics have created chaos, distrust, and deaths.As more and more conflicts break out across Earth, Stevland's children work in the background, in an attempt to control human behavior and perhaps, bring peace to the planet. Stevland took control of Pax. Earth shouldn't be too difficult...