U.S. Robots is planning the production of the LNE series of robots, which are designed for boron mining in the asteroid belt. After a technician neglects to lock a terminal, a factory tourist accidentally reprograms the prototype LNE, wiping clean the structure of the robot's brain, and rendering it a baby in all effects.
Robopsychologist Susan Calvin experiments with it, in the process naming it "Lenny" (and developing maternal feelings for it), and after a month, has been able to teach it a few simple words and actions. She gets emotionally attached to Lenny and realizes that robots can be built that are able to learn, instead of being built for a fixed and specific purpose.
Complications arise when Lenny, unaware of its own force, breaks the arm of a computing technician, which is about to cause widespread "robots attacking humans" panic. However, Susan Calvin manages to exploit the sense of danger to add a new thrill of robotic investigation, just as happens with space exploration or radiation physics.