Bruce Calvin, an engineer, has been let go from his place of employment and considers an unusual want ad in the newspaper. He calls the phone number in the ad and speaks to "Dr. J" about the job. His wife of five years, Frances, nags him about his situation to the point that he quickly leaves the house. At the office of "Dr. J", he meets Dr. Johnson of the Atomic Energy Council. Johnson explains his group has been studying Calvin for some time and they were the casue of him being discharged. They are shortly joined by three other gentlemen, a Naval office, an Army officer, and a civilian. They offer Calvin a large sum of money to undertake a short trip to a nearby planet, a planet that also hosts human life and, in all ways, is a mirror image of their own planet. Johnson insists the two worlds are in lock-step as far as life is concerned -- each planets' eco-systems duplicate the other. They want Calvin to break the linkage by killing his duplicate self on the other world.