In a post-apocalyptic time, Earth has been rendered toxic, and most of humanity has abandoned the planet and colonized one of Jupiter's moons, IO. But young scientist Sam Walden has stayed behind and dedicated herself to finding a way for human beings to survive on Earth. After sending out a radio transmission to see if she can locate anyone else, a man named Micah arrives. He believes there is no hope of survival and intends to take the final shuttle to IO in 48 hours.