After 29 years, Asimov has finally been prodded into continuing his famous Foundation saga: this splendid effort--faithful to the spirit of the original trilogy, while stylistically more expansive and mature--may well be the best yet. The Seldon Plan, designed to create a stable glactic Second Empire, is now half complete. But on the physical-science-based First Foundation, naive, intuitive councilman Golan Trevize notices that the Selden Plan is working a little too well: he realizes that the supposedly destroyed, mental-science-based Second Foundation still exists! So woman mayor Harla Branno secretly orders Trevize to seek out the Second Foundation. And meanwhile, arrogant genius Speaker Storr Gendibal of the Second Foundation, also suspicious of the too-perfect Plan, deduces the existence of an unknown group of mind-controllers: he follows Trevize to forbidden planet Gaia, where shortly Branno and a battle fleet also arrive. The explanation of all this? Well, Gaia, a planetary consciousness comprising humans, animals, plants, and inorganic matter, has engineered the confrontation to force Trevize (he has the knack of making correct decisions) to decide the fate of the galaxy--which involves transcending the efficient but ultimately sterile Selden Plan. Furthermore, behind this windup, there's another surprise (involving--you guessed it--robots) and some absorbing stage-setting for other sequels. After a slowish start, then, the rather talky narrative here develops into grippingly effective drama--with oodles of twisty-turny plot, an engaging cast, and some enjoyably mellow humor (Asimov whimsically manages to work in references to all his previous novels). A grandmasterly performance.