One thousand years later, The Ranger Corps, a peacekeeping organization commanded by General Cypher Raige, comes into conflict with the S'krell, alien creatures who intended to conquer Nova Prime. Their secret weapons are the Ursas, large, blind predatory creatures that hunt by "sensing" fear. The Rangers struggle against the Ursas until Cypher learns how to completely suppress his fear, a technique called "ghosting". After teaching this technique to the other Rangers, he leads the Ranger Corps to victory. Meanwhile, Cypher's son Kitai blames himself for the death of his sister Senshi at the hands of an Ursa. Kitai trains to become a Ranger like Cypher, but his application is rejected due to his recklessness, and Cypher views him as a disappointment. Kitai's mother Faia convinces Cypher to take Kitai on his last voyage before retirement.
During flight, however, their spaceship is caught by an asteroid shower forcing them to crash-land on the now-quarantined Earth. Both of Cypher's legs are broken, and the main beacon for firing a distress signal is damaged. Cypher instructs Kitai to locate the tail section of the ship, which broke off on entry to the atmosphere. Inside is the backup beacon, which they can use to signal Nova Prime. Cypher gives Kitai his weapon, a wrist communicator, and six capsules of a fluid that enhances the oxygen intake so he can breathe in Earth's low-oxygen atmosphere. Cypher warns him to avoid the highly evolved fauna and flora, and be careful of violent thermal shifts. Kitai leaves to find the tail section, with Cypher guiding him through the communicator.
SOURCE:wikipedia