218 prisoners have escaped to Earth from the planet Sar Top in the Migar Solar System, and once on our planet, their life forces take over various human identities. Tracker is the story of Daggon,an alien from the planet Cirron, who has come to capture the criminal fugitives with a device that ensnares their life forces in spheres. Once his mission is over, he has to take them all back to Sar Top.