Mars Mission One, under the command of John L. Black, gets permission from Mission Control to touchdown on the red planet's surface. Once they've touched down, Black takes Henley and Hinkston out, and they confirm that the air is thin but breathable. As they remove their helmets, they heard bird cries in the distance and discover that they're standing on grass. They follow the sounds into a forest of Earth trees and hear the sound of a lawnmower. On the other side of the forest, they find... a typical Midwestern Earth town from decades earlier. Hinkston recognizes it as Green Town, Illinois, where he grew up.
As the men explore the town, they try to determine what is going on. Henley suggests that they somehow went off-course and returned to Earth, but Black points out that their telemetry confirms they are on Mars. Hinkston suggests they somehow went back in time and landed on Earth, but Black again confirms that they saw Mars before they landed. Black calls the exploration ship and tells his lieutenant, Larson, not to let anyone leave until they've determined what's going on.
The three men find no signs of life but discover a house. On the porch is a tennis racket that Hinkston recognizes as identical to the one he had when he lived there. He hears someone laughing in the distance and runs around a corner. Black and Henley follow and discover a tennis court, but no sign of Hinkston. Henley turns and sees his grandfather, alive and well. He runs to the man and embraces him and Henley's grandfather takes him to where his grandmother is waiting. Black goes after them but they disappear after rounding a corner.
Black looks around and hears the sound of people playing baseball in the distance. A figure runs down the street and Black recognizes him as his younger brother Skip. Skip recognizes him and isn't surprised to see his brother there, and invites Black to come home and see their parents. Black goes with him and finds his mother playing piano in their old home. As he embraces her, she gets up and they dance, and she assures him that they're together and nothing else matters.
Later, the other families meet at the Black home and have dinner. As they share a toast, Black wonders how all of their families can be there when they died years ago. The captain wonders if Mars is Heaven, and his mother and the others admit that they don't know. All they know is that they've been given a second chance. A band parade passes outside and Black realizes that the rest of the crew are there, reunited with their dead family and friends. Larson arrives and admits that once they heard the news and found their own loved ones outside, the rest of the crew came to the town. He apologizes but Black says that it's okay. As a suspicious Larson goes back to the ship, Black notes that his lieutenant is an orphan and the only one without anyone in the town. Black's mother insists that it's fine and invites him to join the others for the celebration in their honor.
After the celebration, Black is still trying to make sense of everything. His mother tells him to get some sleep and Skip takes his older brother up to their old room. Black realizes it looks just like it did when he graduated and went to flight school, and points out to Skip that the entire house burned down and Skip died in the fire. Skip tells him to relax and stop analyzing things, and gets ready for bed. Black hesitates and Skip asks him what's wrong. The captain says that he has a theory: the Martians are telepaths. They knew they couldn't fight back with weapons, but they could use their telepathic abilities to destroy the "intruders" by making them think they had landed in a version of Heaven, where their loved ones would be there to greet them... and get them off-guard. Skip points out that would mean that he's a Martian too, and briefly pretends to be one. Black dismisses his suspicions and starts to get in bed, but then thinks about his theory again. He gets up and goes for the door, and Skip asks where he's going. Black says he's thirsty, but Skip knows better and reaches for him with an alien arm...
Later, the surface of Mars lies barren and red, and a line of coffins are neatly lined up. Atop them are the helmets of the Mars Mission One crew. Above, Mars Mission Two prepares to land and tries to contact their predecessors.