After a hive-minded alien race called the Boov conquer the Earth, they relocate the planet's human population—all except for a little girl named Tip (Rihanna), who's managed to hide from the aliens. When Tip meets a fugitive Boov called Oh (Jim Parsons), there's mutual distrust. However, Oh is not like his comrades; he craves friendship and fun. As their distrust fades, the pair set out together to find Tip's mother, but, unbeknown to them, the Gorg—enemies of the Boov—are en route.