Third in Niven's famous Ringworld series (The Ringworld Engineers, not reviewed), set on a colossal space habitat that forms a complete ring, 600 million miles in circumference, around its sun, and comes complete with cleverly engineered days and nights, seasons, oceans, mountains, and what-all. Earth explorer Louis Wu has been trying to evade the surveillance of the Hindmost, a manipulative alien puppeteer who, despite his advanced technology, is trapped on the Ringworld. Nevertheless, the Hindmost observes everything that occurs, especially--in the first (intriguing but largely irrelevant) section--how a motley band of assorted humanoids somehow pool their talents to wipe out a bothersome nest of Vampires. In the second section, exciting but very hard to follow, the Hindmost notes with interest that a powerful Someone seems obsessed with protecting and maintaining the Ringworld. And soon both Louis and the Hindmost are being controlled by a protector, Bram, a Vampire transformed by a virus and a particular diet into a superbeing. Neither is Bram alone--and the problem is that protectors of different species instinctively fight to protect their own species' genes. Someone, however, must take control of the Ringworld to ensure its survival. . . . Notably schizophrenic and confusing but inventive enough that Ringworld admirers will surely wish to investigate.