A general calls Major Alex McAndrews in for a new assignment. He explains that the superhigh-security facility they're in was once a research lab working with wormholes. But "things got out of hand," producing something now hidden behind a thick, steel door. He retracts the door to reveal a blindingly glowing hole in the wall. The general explains four other volunteers already went through and never came back, including Captain Kincaid. Their transmitters cut off after less than ten seconds. The State Department wants it shut down. The Pentagon wants it to stay. The general wants to rescue the others. McAndrews accepts, with his own life falling apart. His wife has left him because of his devotion to duty. He's getting too old to be a test pilot and will soon be assigned to desk duty.
McAndrews dons a space suit. They open the door for him to walk through. He steps through the turbulent white light then finds himself lying on a meadow. He finds a glove from one of the earlier volunteers. Opening his helmet, he finds the air is clean and crisp. Continuing his exploration, he's met by Kincaid and a woman in simple country dress, Berenn. They lead him to a village that they call, "Heaven."
In a communal dining room, the other volunteers join McAndrews. The navigational specialist explains he can't get a fix on the stars. They can't go back because the portal doesn't seem to exist on this side. The villagers are friendly and pledge to make his stay pleasurable. After a while, McAndrews admits to feeling more relaxed than on Earth, where he feels he has nothing left but his duty. He returns one night to find Kincaid's voice recorder. It reveals that the portal exists, but is only visible at night. Kincaid refuses to let McAndrews return to Earth, knowing that the United States government would want to take over. He refuses to let McAndrews pass, even when McAndrews draws his pistol, proving the military's predilection for violence. McAndrews knocks Kincaid aside and runs for the portal. Berenn begs him to stay, but McAndrews feels the pull of duty.
On Earth, McAndrews is debriefed then listens as the officials begin making plans for an invasion. He drops his rank insignia then heads for the portal room. He repeats something Kincaid said to him, "Heaven is a fragile place," then resigns before smashing the equipment and jumping through the portal. With the original portal an accident, the lab will not be able to recreate it.