Martian military commander Ettil Vyre is being held prisoner. The supreme commander, the Assignor, comes to visit him, but Ettil insist that their coming assault on Earth is doomed to failure. The Assignor takes him out for execution but insists that Ettil's wife and son watch the execution. Rather than put them through the shame, Ettil reluctantly to lead the invasion.
At home, Ettil's son wonders why he refused to participate in the invasion. Ettil shows him a treasonous collection of Earth comic books, brought from Earth by Ettil's grandfather. In each one, alien attacks are inevitably thwarted by a strong-jawed youth with a name like Rick. Ettil has concluded that Earthlings have been exposed to such propaganda for so long that they are unbeatable. Ettil's wife, Tylla, comes in and insists that Ettil is wrong and the comic books are just stories, but her husband doesn't believe it.
The Martian warfleet enters orbit above Earth, but the Assignor is surprised to receive a hail welcoming them and inviting them to land and take control of the planet. William Summers, the President of the Association of United American Consumers, invites them to land at a designated town. When the Martians emerge from their ships, they find a marching band and girls with flowers. The Assignor demands their surrender but can't be heard over the music. He and Ettil go to confront Summers and the local mayor, who give them to the Key to Earth. They ask the Assignor to make a conquest speech and he obliges, confused but satisfied that he's won. He wants to kill the people offering the Martians food and drink, but Ettil warns his superior that they can't kill people who welcome them with open arms. After convincing them the food isn't poisoned, the mayor invited them to invade the town, and organized a parade to accompany them. The people cheer them, but Ettil panics when he spots a strong-jawed youth in the crowd. He runs off, and the Assignor assumes that he's a coward.
That night, the Martian soldiers begin to give in to the party spirit and start eating and drinking. The Assignor realizes that he's starting to lose control of his men. Meanwhile, Ettil, telepathically contacts Tylla on Earth, and explains that the strong-jawed heroes of the comics have been replaced by robots pretending to be Earthlings, intent on defeating them with open arms rather than guns. He gives his last regards to Tylla and then tries to save his fellow soldiers. He gets into a confusing conversation with an evangelist, who tries to describe Heaven to him. He assumes she means Mars, and she assumes he means Heaven. When she realizes he's not talking about her Heaven, she takes offense and starts singing hymns as Ettil runs off.
By now, the Martina soldiers have been totally corrupted by Earth customs. They eat pizza, ride motorcycles, gamble, and dance with women. The Assignor is unable to dissuade them. When he sees Ettil, he runs across the street but a car accidentally hits him. The townsfolk take the Assignor's body away and the driver introduces himself to Ettil as Van Plank, a movie producer. They go to a bar and Van Plank explains that he wants Ettil to sign a contract to be a movie star, and appear in a movie showing the Martian invasion. Van Plank has no idea what Martians are really like and has a script in mind where they are typical green-skinned invaders. He wants Ettil to change his name to Joe and act more like an Earthling, offering him $100,000. When Van Plank brings out the contract, Ettil sees his first initial, "R," and discovers that the producer's name is Rick. Realizing that this is the Rick from the comic books, even if he isn't quite so strong-jawed, Ettil flees into the streets and is hit by a car.
When word gets back to Mars of the soldiers' defeat, Tylla sadly tells her son that his father never had a chance.