The X-20 returns from space after disappearing from the radar screens for 24 hours during its 31-hour mission. It crashes in the Mojave Desert and its crew is taken to a military hospital for examination. Major Gart is kept there for treatment of a broken leg. His fellow crewman, Colonel Gregg Forbes, comes to see him and assures him that everything is fine. However, Gart notices that Forbes is acting nervous and asks him what the matter is. Forbes finally admits that something strange has happened, closes the door, and then asks Gart when he left the hospital. He finally says that he left at 9:30 a.m. the previous day, but Gart doesn't remember him leaving with anyone. Forbes shows him a newspaper article and photo that confirms that he and Gart were the two-man crew of the X-20. However, Forbes insists that there was a third man, Colonel Ed Harrington.
Gart has no idea what Forbes is talking about, and points out that there are only two beds in the hospital room, his and Forbes'. Forbes insists that he and Harrington left the previous day, even though Gart doesn't know anyone called Harrington. Forbes explains what happened. The previous day, Forbes and Harrington talk to Gart and wish him well before going to a bar that night. The bartender knows who they are from the newspaper showing their photo. Harrington drops his glass as he is suddenly overcome with a strange sensation as if he wasn't quite there, and goes to the phone book to call his parents in Iowa. When he collapses in shock, Forbes checks on him and Harrington explains that his parents have no idea who he is. He wonders if something, or someone, somehow let them return to Earth when they weren't supposed to, and now it is making up for its mistake. Forbes tells him to wait there while he gets a drink for his friend. When he returns, he discovers that Harrington has disappeared. The bartender has no idea who Harrington is and doesn't remember him, and the glass that Harrington dropped has disappeared as well.
Panicking, Forbes goes home where his wife Amy is waiting for him. She reminds him that he was supposed to pick her up at the bus depot but he never arrived. He remembers writing down that he and Harrington would meet her, but when he checks the notepad, Harrington's name has disappeared. Amy doesn't know who Harrington is either. When Forbes calls his superiors, they don't know who Harrington is. Forbes runs off in a panic and goes back to the now-closed bar, begging Harrington to come back.
Forbes finishes his explanation but Gart still doesn't know who Harrington is. Forbes wonders if Harrington is right and something is taking them back. He feels the same sensation that Harrington did and looks in the mirror… and discovers that his reflection has disappeared. He runs out into the hall but when Gart goes after him a second later, Forbes has disappeared entirely.
A nurse comes by and has no memory of Forbes. Gart now only has one bed, and the newspaper article only shows that he returned from a solo flight. Seconds later, a nurse returns with a medical officer and informs her superior that the ward is empty and available for future use. Gart is gone. And in the hangar, the X-20 disappears as well, leaving no trace of the ill-fated mission.