The third and weakest of
Larry Niven's
Ringworld series of novels. it was first published in 1996, 24 years after the first one,
Ringworld.
Plot summary: NB: Spoilers ahead.
A few years after the events of The Ringworld engineers, Hindmost is still safe in his ship, whiling away the hours practicing aerobics, while Louis Wu and Chmeee sail a giant ship across the great ocean.
Natives of the Ringworld, supposed dead in the flaring of the sun, are found alive and well and fighting vampires. Hindmost's insistence that his computer systems allowed more precise control than Teela Brown gave him credit for, Louis Wu refuses to believe this, and has decided to grow old and die for his part in so many deaths.
He is convinced when he sees recent video footage of them, and consents to be rejuvenated. Hindmost now has remote sensors all over.
Much happens, little of it important. A protector surfaces in the Ringworld control center. He was a vampire. They call him Bram. Other protectors, of various Ringworld races, are at work on the rimwall, constructing and mounting new attitude jets. Kzinti and Earth government ships appear but are shot down, but not by Hindmost, who had effective control of the repair center until Bram showed up. Bram begins to kill of the protectors on the rimwall.
Bram is eventually defeated when Loius Wu lures a ghoul (nocturnal, carrion-eating sapient hominid) into the repair center, where he becomes a protector and defeats Bram. Some Ringworld history becomes clear at the end: Bram (and his mate) toppled the Ringworld's previous protector a couple of thousand years ago, by waiting in the repair center, and the striking when he arrived to do deflect a large meteorite. The meteorite impacted, causing the Fist of God (and much loss of life). Loius Wu thus judges Bram unfit to protect the Ringworld The remaining protectors begin to negotiate and make peace.