A scientist named Jan Cornelius, who specializes in mind-linking technology using esprojectors, travels to a space station orbiting Jupiter. His goal is to figure out what is causing some of the esprojector technology to explode. The technology mediates the linkage of minds between the intelligent puppet lifeform on the planet and Ed Anglesey who is controlling it. When Anglesey is controlling Joe, the humanoid is energetic and ready to take on the elements. He is the only human-engineered intelligent lifeform on the surface and the hope is to build a colony of them in the future. That is difficult though because of money and the harsh conditions on the planet. Anglesey is starting to notice that his human body is experiencing the toll of what Joe's body is doing on the surface of Jupiter. Anglesey is an ill-tempered man who lost the use of his legs in an accident. Viken, another scientist on the station discusses matters with Cornelius. As Cornelius interacts with Anglesey, it becomes clear that neither one particularly likes the other. Cornelius suggests that the technology could be malfunctioning because Anglesey secretly doesn't want to be on Jupiter or because of some other psychological reason. He suggests this cautiously to Anglesey who listens, but tells Cornelius he is wrong. Joe is starting to get lonely on the surface and wants more humanoids sent down, which is not supposed to happen for a while. Anglesey convinces Viken and others to move up the plan and Cornelius supports him. Talking with Viken, Cornelius admits that he supports the plan because it will make Anglesey distracted and he will be able to link himself to both Anglesey and Joe to see what is really going on. He is beginning to suspect that perhaps Joe is taking over Anglesey's mind, which is why - as Viken tell him - Anglesey is more withdrawn than he was at first.

More ships with humanoids are sent down to the surface. Cornelius establishes the link, but is surprised to find that Joe recognizes him there and he can still read Joe's thoughts. If the alien brain had taken over, as he suspected, he would only hear scattered thoughts. It turns out that Anglesey has become Joe and Joe has become Anglesey. They are happy together in Joe's body. Joe expels Cornelius from the mind link, which is also affecting Anglesey's body on the space station negatively. Cornelius removes Anglesey's body from the technology. The doctor tries to save him, but Anglesey dies. Viken is upset because he thinks the project is a failure. He says no one will want to participate in a human and Jovian link, but Cornelius contradicts him. He tells him that Anglesey was happy to be in a strong body and people whose bodies are not functioning the way that they want will be happy to gain another body on Jupiter.