In the process of trying to develop a hyperdrive, US Robots most advanced positronic brain—“the Brain,” in fact—is called in to help. It comes up with a solution, a ship is built, and Gregory Powell and Mike Donovan are called in to test it. Despite Susan Calvin’s precautions, however, the Brain is not entirely stable and has decided to play a practical joke on its two astronauts.
This unique Susan Calvin/Powell-and-Donovan story isn’t one of the strongest of Asimov’s earlier robot stories. The surreal trip Powell and Donovan go on is interesting and fun, however, and largely redeems it in my sight, so that although I wouldn’t rate it as high as “Reason” or "Evidence,” it ranks solidly in the second-tier.