Mr. Heinlein's latest book is set in the far distant future when even space ships have been outdated and man is travelling by torchship. Earth has a serious population problem, pinpointed by the predicament in which the twins Tom and Pat Bartlett find themselves when they by chance go to take some tests for colonization in a distant system. To complicate matters, the boys find they can read each other's minds and that this is directly in line with the planning board's project, to have halves of telepathic twins go off to the new world so that people on Earth will know what is going on. First Pat, the dominating twin, is the one to go, but an accident puts Tom, the narrator, in his place. Heinlein is at his best in combining science with fiction in what follows, for Tom stays young under the theory of relativity and the brother rivalry remains to be worked out by remote control. A catchy story that spoofs humanity's foibles and comments on them endearingly, this strengthens Heinlein's niche in the science fiction field yet further.