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,