The story concerns five diverse students who attend a philosophy seminar. The professor, Arthur Frost, explains that he learned how to use his mind to go back in time and correct a bad mistake in his life. Using hypnosis he lets them travel to alternate worlds of their choice. All the students disappear except one, Howard Jenkins. The hypnotic suggestions had no effect on him, because he could not at all believe that it was possible. He is distraught at the disappearances, but the professor assures him that they all received a hypnotic suggestion to come back in two hours.After two hours the students start coming back, and they tell their stories. In each case, the subjective time elapsed was much longer than two hours. Some of them spent a whole lifetime in the alternate world.