A space creature hatches from an egg that Hun-i picked up on the summer beach. The Lee-an couple, the parents of the creature, come to Earth accompanying Lu-ci-na, a space outlaw, on the condition of helping him find their son Lee-an-ppi, who was sent to Earth long ago. For the sake of Earth's endangered fate, Dr. Kim orders Hyung-rae and Dae-il to confront it with the Thunder Operation Cannon 3. As Earth's crisis escalates, Ure-mae appears, defeats the outlaw Lucifer and his henchmen as well as Robert Kanga, dramatically saving Earth. Lee-an-ppi, after his mother is killed by Lucifer's gang for not cooperating, heads to his home planet with his father Lee-an. Hun-i's eyes well up with tears as he waves to Lee-an-ppi disappearing beyond the atmosphere.