This is the third and last book in the original Foundation Trilogy, published in the 1950s. The book is divided into two parts, just like the previous one, the first detailing the search for the Second Foundation by 'The Mule' who became undisputed ruller of the Galaxy (Milky Way) in the previous book, and the second, after the downfall of the Mule, gives an account 50 years in the future about the search for the Second Foundation by a group of scientists from Terminus, the First Foundation. The book becomes slower and less exciting in the second part, as most of the plots and twists have happened already, and this was to serve as a conclusion of the Foundation saga (some 400 years into the 1000 years of barbarism predicted by Hari Seldon, before the second Galactic Empire rises).
The first part of the book details the search for the Second Foundation by Capt.Pritchard, now converted by the Mule into an unquestionably loyal soldier, and another rising star of the political scene at Kalgan, the seat of the 'First Citizen' of the Galaxy, the Mule. The Mule follows both of these people as he trusts no one. Pritchard's companion discovers what he thinks is the planet where the Second Foundation is, while they are doing research at the Imperial Library on Trantor, and they head off for 'the other end of the galaxy' as Hari Seldon described the place where the Second Foundation is to be found. Once there the Mule catches up with them, having them followed the entire time, and destroys the planet they were intending to explore and uncovers Pritchard's companion as a Second Foundationer.
However, the second foundation is on their tracks as well, and the 'First Speaker', the leader of the Second Foundation, converts the Mule to abandon his search and live the remaining few years of his life in peace. In the second part, we are now 50 years in the future, and the grand daughter of Beida who stopped the mule in the 'Foundation and Empire', Arcadia, is now 14 and her father is developing ways to discover the Second Foundation, one being sending one of his collaborators to Kalgan to look through the Mule's files in his palace. Arcadia catches a ride on the ship and gets introduced to the ruler of Kalgan, who also carries the title 'First Citizen' though he doesn't rule the galaxy, but a handful of planets around Kalgan and has grand plans of conquering the Foundation and the galaxy with his fleet. However his mistress is placed there by the Second Foundation and she gets Arcadia out of Kalgan on onto Terminus from where she sends a message to her father who figures out that the Second Foundation is on Terminus, and finds a traitor among his group who then confesses and about 50 second foundationers are rounded up.
All of this is an elaborate plan of the second foundation who have planned this since Arcadia was born 14 years ago and converted her to give those exact clues to her father, and sacrifice 50 people in order to hide the real location and purpose of the second foundation, to form the ruling class of the Second Empire which Hari Seldon expected to be the next step of the human evolution where humans develop a form of hive mind, being emphatically connected to everyone else. All in all, a good reading, but slower and not as exciting as the previous couple of books. Asimov wrote two more sequels to the trilogy, but then ran out of ideas for the future of the Foundation, so instead wrote several prequels to the trilogy, where Hari Seldon is the main character, partly autobiographically modeled on Asimov himself.
