It’s 23 years since their last adventure. Prill was taken by Earth authorities shortly after her arrival on Earth and Louis becomes a wirehead. Louis and Speaker (now Chimee) are kidnapped by Hindmost, the puppeteer mate of Nessus. They are taken to Ringworld in search of a matter transmutor so that Hindmost can return to his homeworld(s) and reestablish his political authority. There is no such thing, but Louis and Chimee continue the deception. In order to force Hindmost to commit to saving Ringworld, Louis destroys the hyperdrive motor on their spacecraft making FTL travel impossible. This story has a bit more plot to it than Ringworld. They meet a number of different hominid species while searching for the Repair Center. The quest for the Repair Center is at first to look for transmutor technology which Hindmost seeks, but Louis had always intended upon saving Ringworld from eventual destruction as its orbit around the sun is unstable. The instability was likely due to most/all of the the Bussard ramjets being taken off the structure and used in spacecraft by the City People (the most techologically advanced inhabitants). The impact which resulted in the Fist of God puncture may have also contributed to the instability. The different cultures of the inhabitants of Ringworld are only briefly touched upon, which is a shame. More depth in this area would have improved the story. More details are provided about the Pak Protectors and the tree-of-life and origin of humanity. Along the way about two-thirds in, Louis picks up two City People (by accident), a woman and young man who become part of the party seeking a way to repair the Ringworld orbit. There’s a lot mating. It’s not explicit, but much of it doesn’t seem to add to the story. Rishathra, or a kind of contractual sex between hominid species is used frequently.For a while Chimee departs to the Map of Kzin to mate with as many female kzin as possible. Dunno why (why not?). In the end, the Repair Center is hidden under the Map of Mars where Teela Brown is encountered. She has transformed into a Protector via the tree-of-life. Both she and Louis know that to save the Ringworld 5% of the population (billions) must be sacrificed to excessive radiation from the sun in order to boost the power of the remaining attitude control jets that the Protector had directed to be reinstalled. Instinctually she cannot kill this many inhabitants and tries to prevent Louis and party from doing so, though in a fashion where she hopes for her own defeat. This combination of superior intelligence bound by strong instinctual motivation I find is difficult to reconcile. How can a protector be effective if the logic of the “good of the many” is never followed? Teela is defeated, 5% of the Ringworld is awash in a radiation burst (the part of the world they had adventured in), but the Ringworld is saved. Hindmost, Chimee, Louis and the two City People remain since they have no means to get back to Known Space. Nominated for the Hugo. The best things about the Ringworld books is the sense of scale. Both in size (3 million Earths!) and time (evolution has diverged the hominids and kzin species substantially from those in Known Space).
(Amazon) The Ringworld Engineers