It's been 25 years since the first humans landed on the planet Mars. Shortly after their landing, all communication was lost, so now another craft is sent, and when they arrive, they discover that the humans are living in community with Martians, and that two children have been born on mars. One of the children is Valentine Michael Smith, or Mike, who quickly becomes famous (they call him "The Man from Mars"). In a series of legal battles on the boy's behalf, Smith inherits a tremendous fortune. As the only human, he also has the legal right to claim ownership of the planet Mars. His fate is settled on his behalf—he will be an ambassador to the new planet Mars and the Martians.
Meanwhile, Mike is just a child, still hospitalized, learning to adapt to earth air, learning the basics of human civilization and geopolitics (his life on Mars was radically different in every regard). The legal battles in Mike's favor came with the help of US Secretary General, Joseph Douglas, so a reporter named Ben Caxton enters the story as a whistle-blower in waiting, trying to uncover something nefarious. Ben has an ex-girlfriend who works at the hospital, and he gets her help to spy on the hospitalized child. Ben accidentally spooks the authorities, so they abduct him, but Jill (the girlfriend) escapes with Mike. Mike uses Martian magic to vanish into another dimension.
When Jill and Mike reconvene, she takes him to Jubal Harshaw, an important Renaissance man with successful careers in art, philosophy, writing, law, and medicine. Jubal is so exorbitantly wealthy that he has a mansion with a full staff. He agrees to help them, and Mike lives there, learning daily about humanity and the earth. He is fascinated by human religions. One day, the police find them and come to the house to arrest Jubal and to abduct Mike, but Jubal talks to General Douglas directly and the police are called off. To divert unnecessary political attention from Mike's life (until he's older), Douglas and Jubal agree to change the ruling about Mike's legal claim to ownership of Mars. Mike continues his religious education.
Mike, Jubal, and Jill travel to a religious cult for Mike to learn about, called the Fosterites. The Fosterites are popular among celebrity culture, but they're a cult. When their cult leader tries to manipulate Mike into joining the cult, Mike makes him vanish into thin air. Later, Mike feels he over-reacted. He understands that he has exceptional psychic abilities compare to the earthlings, and he sets about to discover enlightenment on the planet. Another Fosterite, Patty Paiwonski, attempts to convert Mike, but Mike reveals his identity and she begins to worship him as a prophet of God. We also learn that Jill has been learning basic Martian words and phrases, and that Mike is helping her unlock her own psychic abilities.
One day, Mike realizes that all he has to do to fix the planet is to start a religion. He founds a church and calls it The Church of All Worlds, and he sets it up to be a cultural phenomenon. He founds a core group in the church which he calls, "The Ninth Circle," and those core members live with Mike and practice doing magic with Mike. They are polyamorous and sexually promiscuous. Ben re-enters the story, freed by the police now, and he joins the cult after some deliberation. Jubal and Mike start to have serious disagreements.
Mike explains after an argument with Jubal that he always intended for his religious message to be about happiness, and he wonders if the earthlings are committed to unnecessary strife. Outside, Mike's persecutors have formed into an angry mob. He presents himself to them, and they murder him. In heaven, he is honored as an archangel alongside other "heretical" prophets.
