In the future on a human-populated space colony, Nova Prime, the S'krell extraterrestrial race attempts to take it over with creatures called Ursas, which hunt by "sensing" fear. Peacekeeping organization The Ranger Corps defeat them with a fear-suppressing technique called "ghosting," but not before a Ursa kill Senshi, the daughter of Rangers' leader Cypher Raige. Kitai, Cypher's son, blames himself for Senshi's death. He trains to become a Ranger like Cypher, but is rejected when he applies. Kitai's mother Faia convinces Cypher to take Kitai on his last voyage before retirement. During flight, however, their spaceship is caught in an asteroid shower, causing them to crash-land on Earth, which the humans evacuated a thousand years ago due to an environmental cataclysm.