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Aliens from the planet Zanti send their criminals to Earth and insist that they be kept in an isolated area outside of all human contact. However, the situation becomes complicated by the intrusion of outsiders.
A government agent infiltrates a secret organization known as the "Invisibles" who attach parasites to the spinal chords of their victims. And, in doing so, they hope to take over the world!
After finding an ancient man by the side of the road, Wade Norton finds a strange house where some people are kept prisoner (and ageless) by an alien intelligence.
Two Earth people are transported to an alien planet, along with two aliens. They are told by their abductors that they will fight each other to the death. The stakes are high: the homeworld of the losers will be destroyed slowly, for the further amusement of their captors.