The Earthman
Elijah Baley (the
detective hero of the previous
Robot books) has died nearly two centuries earlier. During these two centuries, Earth-people have overcome their
agoraphobia and resumed
space colonization, using
faster-than-light drive to reach distant planets beyond the earlier "
Spacer" worlds. Their inhabitants, calling themselves "Settlers" rather than "Spacers", revere Earth as their mother-world. Baley's memory remains in the mind of his former lover,
Gladia Delmarre, a long-lived "Spacer" who uncharacteristically relocated from the spacer world of
Solaria to
Aurora. Gladia's homeworld and the 50th-established of the Spacer planets, Solaria, has become empty of all human inhabitants, although millions of robot servants remain. A seventh-generation descendant of Baley's, Daneel Giskard ('D.G.') Baley, gains Gladia's help in visiting Solaria, to investigate the destruction of several "Settler"
spaceships that made landings there and to capture the presumably unsupervised robots. Gladia is accompanied by the positronic robots
R Daneel Olivaw and
R Giskard Reventlov, both the former property of their creator, Dr
Han Fastolfe, who bequeathed them to Gladia in his
will. R Giskard has secret
telepathic powers of which only R Daneel knows. At the same time, Daneel and Giskard are engaged in a struggle of wits with Fastolfe's rivals: The
roboticists Kelden Amadiro and
Vasilia Aliena, Fastolfe's estranged daughter. Frustrated by his series of failures, Amadiro accepts an ambitious and unscrupulous apprentice, Levular Mandamus, who plans to destroy the population of the Earth by a newly developed weapon, the "nuclear intensifier", with which to accelerate the natural
radioactive decay in the upper crust of the Earth, thereby making the surface of the Earth radioactive. R Daneel and R Giskard discover the roboticists' plan and attempt to stop Amadiro; but are hampered by the
First Law of Robotics, which prevents them from a direct attack on Amadiro. Daneel and Giskard, meanwhile, have inferred an additional
Zeroth Law of Robotics: It might enable them to overcome Amadiro, if they can use their telepathic perception of humanity to quell the inhibitions of the first law. When Vasilia accuses Giskard of telepathy (earlier created by herself), Giskard is compelled to manipulate her mind to make her forget about his telepathic powers. The two robots locate Amadiro and Mandamus on Earth, at the site of
Three Mile Island Nuclear Generating Station in
Pennsylvania. After Amadiro admits their plans, Giskard alters Amadiro's brain (using the newly created Zeroth Law); but in so doing, threatens his own. Now alone with the robots, Mandamus claims that his intentions were to draw out the radioactive catastrophe over many decades, rather than the mere years that Amadiro wanted, and Giskard, believing it best for humanity to abandon the Earth, allows Mandamus to do this (resulting in the situation depicted in
Pebble in the Sky), and deprives Mandamus of the memory of doing so. Giskard predicts, correctly, that by forcing humanity into leaving the Earth, vigor will be reintroduced into humankind and the new Settlers will populate space until all the governments of the interstellar colonies form a "Galactic Empire". Under the stress of having violated the First Law (in accordance with the Zeroth Law, but with the predicted benefit to humanity being uncertain), R Giskard himself suffers a soon-fatal malfunction of his positronic brain, but manages to confer his telepathic ability upon R Daneel. ==Novel==