The first book was all about Seldon's plan. Everything went according to plan, as they were supposed to, and the entire book was merely about how those plans came to pass. How at three different times of crises those plans were executed.

The second book in the series was all about Seldon's plan as well. Everything went according to plan, as they were supposed to, and the entire book was merely about how those plans came to pass. Slightly different kind of crises but in the end it all worked out. Except that we barely got to see what really was happening on Terminus itself.

Then there is this third book, which of course was all about Seldon's plan as well, except that the plan was failing now. The calm assurance that everyone had in the plan was killed off in an anon and only hysteria and uncertainty survived. All because somewhere in the universe a gene decided to mutate, and that just can't be taken in to account when one deals with statistics. Individuals do not matter, except that in this case one did and the plan almost failed.