Second Foundation

The final novel of the original Foundation series is a mother. Suspenseful, filled with intrigue, and building on the theme of mentalics and emotional control and manipulation as an innate trait of the human mind. Asimov finally reveals the location of the elusive Second Foundation, but only after the final defeat of the Mule and an elaborate heist to fool the leaders of the First Foundation about 50 years after the fall of the aforementioned Mule. This final chapter in the original trilogy really does illustrate the inner workings of Seldon's Plan and the threat posted by individuals and unaccounted for anomalies like the Mule. Indeed, the Second Foundation's possession of mentalic powers, plus the physical sciences of the First Foundation, will both be necessary to usher in the Second Empire. 

But, the Galaxy is not yet ready for outright rule by the psychologists of the Second Foundation, which must remain shrouded in secrecy until a future date. Of course, the Second Foundation is hiding in plain sight and must rely on guile to defeat the more powerful foes of the First Foundation and the Mule. Needless to say, the Second Foundation's guiles, emotional and political manipulation, and sleights of hand succeed. It becomes clear how, despite all their predictions and careful editing of the Seldon Plan, deviations caused by individual actions had a large impact on nearly ruining the chances of long-term success. 

In short, human agency and free will coexists, alongside control from forces above that limit or shape the decisions made by Arkady, Darrell, and other characters in the novel. While the novel ends with several centuries left before the predicted emergence of the Second Empire, it seems to posit a future grand empire based on a fusion of the social and physical sciences as the path forward for human evolution when a new age of humanity will rule the Galaxy.