Isaac Asimov's Robots and Aliens 2: Intruder (Book 3), Alliance (Book 4)

A man without memory, tied by blood to a city of robots. At his side, a mysterious woman whose life and memory he saved, whose love he has won for a second time. His name is Derec; hers is Ariel. In intruder, Derec Avery has at last returned to the original Robot City, only to discover that it has been reprogrammed in ways that do not make sense. Together with Derec's love, Ariel, and his father, he must find and defeat the Watchful Eye, the strange force that has bent the city to its own ends. Can they solve the new mystery of Robot City before it comes tumbling down around them? In Alliance, Robot City has been restored, but can it last? Three shape-changing, renegade robots threaten to destroy the city, but are they really capable of disobeying the Three Laws? Derec and Ariel must convince the renegades that an alliance, not a robot revolution, is in their best interest-but will they succeed? The futures of mankind and robotkind wait for the answers!