A Martian woman has dreams of a rocket coming down from the sky, containing a light-skinned, blue-eyed creature named Nathaniel York. Her husband is weary, and when the rocket lands, he shoots the men. All over Mars, people begin to hum Earth tunes and have strange dreams. When a second rocket lands, the astronauts get out and explore. They say they are from Earth, but everyone thinks they are crazy people who have hallucinated their rocket. Thus, they are all shot by a psychologist. Meanwhile, on Earth, a crazed taxpayer tries to board the third rocket to Mars, but he is denied. When it lands, the astronauts find themselves in an ideal small American town. They meet their dead relatives and split up to have dinner with lost parents and brothers. Captain John Black goes to bed next to his long-lost brother, only to realize that it is probably all a Martian trap. His "brother" kills him before he can leave the room.
A year later, a fourth expedition lands, and it is successful. Almost all the Martians have died of chicken pox, apparently acquired from one of the previous expeditions. Captain Wilder lets his men drink and dance, but this angers the archaeologist in the crew, Jeff Spender. Spender feels humbled by the great Martian civilization and wants the rest of the crew to be dignified. He goes crazy and tries to kill the crew; Wilder reasons with him and is somewhat sympathetic, but finally has to shoot him.
Settlers begin to arrive on Mars, drawn by the promise of work. Benjamin Driscoll's job is to plant trees. One morning, after it finally rains, he turns around and sees that the once-barren landscape is now covered with green. Another settler, Toma's Gomez, experiences an even stranger event when, in the middle of nowhere, he runs into a Martian. They cannot touch each other, seeming to exist on different time-planes.
The first settlers are rough, but they build churches in little shantytowns just like American towns. Sometimes, their children sneak off to Martian ruins, where countless carcasses are still being cleaned up. They play songs on the Martian bones. Back on Earth, all the Negroes in the American South have banded together to emigrate to Mars. As they walk in an exit parade through one city, a racist white man, Mr. Teece, tries to stop them, but they band together to pay all debts. The racist man weeps and feels lost without them.
Back on Mars, a man named William Stendahl has constructed a recreation of the House of Usher. He is bitter that the government has made tales of fantasy illegal. He invites the top politicians responsible for this to a party, at which they are systematically killed.
Mars is eventually flooded with retirees. One couple misses their dead son, until one day Tom shows up on their porch. He is actually a Martian who changes shape according to the desires of those around him, and when he goes to town, many people fight over him, each thinking him to be a different person.
News comes from Earth that atomic war is imminent. Sam Parkhill, a man from Captain Wilder's expedition, is proud of the hot dog stand he has just opened. Suddenly, some Martians approach him, but he kills them. Finally, he is subdued. They hand over to him their deeds for half of Mars. He is bewildered, until later that night, when he sees Earth burst into flame. All over Mars, people watch, and a radio signal comes to Mars with the words "Come Home." Everyone evacuates. One man, named Walter Gripp, who lives in the mountains, is left behind. He searches desperately for a woman to keep him company, but when he finds Genevieve Selsor, she is disgusting.
Twenty years pass, with Hathaway living with his family in a shack on Mars, waiting for a rescue. Finally, a rocket lands. It is Captain Wilder, back from exploring Jupiter and Pluto. He doesn't understand why Hathaway's family has not aged, and as Hathaway suddenly dies of a heart attack, he realizes that they are robots.
Back on Earth, a fully automated house is dying. Its occupants died long ago, in the nuclear war, but the house kept washing and playing music every day. A falling tree bough catches it on fire. On Mars, a family has escaped the wasteland of Earth. Dad tells his sons that they are Martians now. Soon another family will arrive, with girls. Dad is happy to have left the foolishness of Earth.