The last part of the original trilogy, in which we finally find where the Second Foundation is.
After the first two books, what's impressive is how Asimov keeps the good ideas coming. The story of the Mule takes up most of the first part of the book (I'd sort of remembered him as being wholly contained in the second, so it was good to find that there was more to tell about him). Uniquely powerful though he is, in the end he is defeated by the Second Foundationers, and the way that happens is once again like a locked-room mystery that Asimov is able to set and then solve.
Again, a theme in the book is mind-control: the altering of one's desires: of those "converted" by the Mule, who know what's happened, but have no wish to be otherwise, and those who have been tampered with by the Second Foundation, who don't always know that it's happened, and can't believe it when they find out. The whole idea is delicious, and Asimov makes the most of it.
The ending was nicely done, with a series of people all putting forward plausible theories as to the location of the Second Foundation, and then having those plausible theories equally plausibly refuted.
I suppose I ought to read the other Foundation books now...
Completed : 28-Jun-2006