"Second Foundation" is the third book in Isaac Asimov's Foundation series, published in 1953. It continues the story of the Foundation and its struggle against the decline of the Galactic Empire. The narrative focuses on the mysterious Second Foundation, a group of mentalics who possess advanced psychic abilities, and their efforts to guide the future of humanity. The plot revolves around the search for the Second Foundation by various characters, including the Mule, a powerful mutant who threatens the stability of the Foundation. The book explores themes of power, manipulation, and the importance of knowledge in shaping society's future.