The Computer Connection by Alfred Bester
A band of immortals recruit a new member, the brilliant Cherokee physicist Sequoya Guess. Dr. Guess, with the group's help, gains control of Extro, the super-computer that controls all mechanical activity on Earth. They plan to rid Earth of political repression and to further Guess's researches-which may lead to a great leap in human evolution to produce a race of supermen. But Extro takes over Guess instead and turns malevolent. The task of the merry band suddenly becomes a fight in deadly earnest for the future of Earth.