Unemployed engineer Bruce Calvin is at home and checks a newspaper ad offering a job for high money requiring "nerve." Bruce paces nervously and then calls the number again. He finally gets an answer and the man at the other end, Dr. Ferris Johnson, assures Bruce that the job is still available. Johnson asks Bruce to come by immediately despite the fact that it's late and Bruce agrees. Once he hangs up, Bruce starts to take a drink out of habit but then sets its aside.
Frances, Bruce's wife, comes in and he tells her that he has a job interview. She's unhappy that he's been unemployed so long and Bruce admits that he has no idea why he was fired after eight years with his company. Frances complains that she's married a failure and Bruce, refusing to put up with her constant carping, leaves for the interview.
When Bruce arrives at the office, Johnson introduces himself and explains that he's with the Atomic Energy Control. He explains that they've been expecting Bruce to call for days and that they want him to participate in an important scientific experiment in return for $250,000. Johnson tells Bruce that he won't be harmed or changed, and that once the experiment is over he can return home.
Bruce wonders how much the time the job requires and Johnson tells him that he'll have to train three works. The doctor explains that Bruce has been under observation for more than a year, and he has a blood type that makes him perfect for the experiment. Bruce wonders what happens if he refuses and Johnson advises him not to do it. He admits that they had him fired for his last job so that he'd have no choice but to accept their job offer. When Bruce asks what it's all about, Johnson tells him that they plan to send him to another planet.
Dr. Gorham and a military committee arrive and introduce themselves, and Gorham swears Bruce to secrecy. Once Bruce agrees, Gorham explains that they have discovered another planet and that it has life and matter exactly the same as their world. Bruce is ready to leave, thinking they're pulling his leg, but Gorham orders him to stay. The doctor then continues, explaining that everything on the other planet is a duplicate of their own. Both planets know of the other and have been setting remote drones to investigate their counterparts.
Bruce demands to know why they want him and Johnson tells him that they're going to send him in a one-man spaceship to the other planet. He will then enter his counterpart's home, complete a short mission, and return. The government believes that both planets will destroy each other rather than let the other exist. Bruce will place poison somewhere in his counterpart's home where he will inadvertently consume it. Once the synchronicity is destroyed between the two worlds, their world's future will be safe. Bruce is reluctant to commit murder, but Johnson and Gorham pressure him with how great his life can be until Bruce finally accepts their offer.
When Bruce returns home, he tells Frances that he has a job but refuses to tell her the details. All he will say is that it's a government job and that the continuing existence of their world depends on his success... their world of Jupiter.
Johnson and Gorham run a series of tests on Bruce for the next three weeks. They come to their conclusion and Gorham explains that the spaceship is on autopilot. When he is ready to return, all Bruce has to do is hit the reverse power switch. Gorham gives Bruce the vial of poison and $100,000, with the balance due when he returns. The ship is ready to depart and Johnson assures Bruce that when he returns in 24 hours, he can tell Frances everything.
Bruce departs in the ship and it lands successfully on Earth. Bruce goes to his counterpart's house and discovers that it is identical, right down to the curtains. When Frances takes a phone call in the next room, Bruce sneaks in through the window and puts the poison in a decanter of whiskey. The alternative Frances comes in and gives Bruce his clean shirt. He examines her arm, amazed at the similarity to his wife, and then says that they'll talk the next day and runs off.
Back on Jupiter, Bruce tells Johnson that his mission was a success. When Bruce worries that he committed murder, Johnson tells him that he merely killed a shadow, a duplicate, and pays him the remaining $150,000.
Bruce returns home and decides to pour himself a drink in celebration. Frances comes in and complains about his lack of work until Bruce shows her the two checks for $250,000. As he takes a sip of whiskey, Frances comments about how he was there the previous night. Bruce confirms that Frances gave his counterpart a clean shirt and then calls Johnson and tells him what happened. He demands to know if his counterpart could have done the same thing he did, and Johnson realizes that the two worlds are linked at every level and Bruce's counterpart carried off the same mission.
Shocked, Bruce hangs up on Johnson and goes to the mirror to look at himself. Frances wonders if the checks are good and, disgusted, Bruce tears them up. He starts to collapse, dying, and breaks the mirror with a vase.