The wave of expansion from Earth to other planets is gaining strength, and conflicts arise between cosmonites (residents of the Outer Worlds) and settlers (descendants of Earthlings). Gladya, a cosmonite woman whom Elijah Bailey once shared sincere love with, is still alive—since cosmonites live three to four centuries. Alive too is her enemy, Dr. Amadireo, who, after the death of Dr. Han Fastolfe, has again set out to take revenge on Earth, which has already settled many planets.
By Fastolfe’s will, Daniel and Giskar passed into Gladya’s possession. Both robots traveled together with their owner to Solaris, Bailey-Mir, and Earth. During this journey, they formulated “the Zero Law of Robotics.” Unable to endure the requirements of this law, Giskar managed to reprogram Daniel, transferring his mental abilities to him and implanting the Zero Law into him.