Gold

He was the analog—the mirror image—of the Mayor of Terminus, who ruled over the First Foundation. But they were different in every respect. The Mayor of Terminus was known to all the Galaxy and the First Foundation was therefore simply “the Foundation” to all the worlds. The First Speaker of the Second Foundation was known only to his associates.

And yet it was the Second Foundation which held the real power. The First Foundation was supreme in the realm of physical power, of technology, of weapons. The Second Foundation was supreme in the realm of mental power, of the mind, of the ability to control. In any conflict between the two, what would it matter how many ships and weapons the First Foundation controlled, if the Second Foundation could control the minds of those who controlled the ships and weapons?

But how long could this remain a secret?

From Foundation's Edge

A millennium into the future, two advancements have altered the course of human history: the colonization of the Galaxy and the creation of the positronic brain. On the beautiful Outer World planet of Solaria, a handful of human colonists lead a hermit-like existence, their every need attended to by their faithful robot servants. To this strange and provocative planet comes Detective Elijah Baley, sent from the streets of New York with his positronic partner, the robot R. Daneel Olivaw, to solve an incredible murder that has rocked Solaria to its foundations. The victim had been so reclusive that he appeared to his associates only through holographic projection. Yet someone had gotten close enough to bludgeon him to death while robots looked on. Now Baley and Olivaw are faced with two clear impossibilities: Either the Solarian was killed by one of his robots unthinkable under the laws of Robotics or he was killed by the woman who loved him so much that she never came into his presence!

A puzzling case of roboticide sends New York Detective Elijah Baley on an intense search for a murderer. Armed with his own instincts, his quirky logic, and the immutable Three Laws of Robotics, Baley is determined to solve the case. But can anything prepare a simple Earthman for the psychological complexities of a world where a beautiful woman can easily have fallen in love with an all-too-human robot…?

Long after his humiliating defeat at the hands of Earthman Elijah Baley, Keldon Amadiro embarked on a plan to destroy planet Earth. But even after his death, Baley's vision continued to guide his robot partner, R. Daneel Olivaw, who had the wisdom of a great man behind him and an indestructable will to win…

A complex tale of time travel and time paradoxes, considered by some critics to be Asimov's finest work.