A new planet has been discovered, unlike anything known to man or alien. The Ringworld is not a natural planet, but was constructed in the distant past over an enormously long period of time. The Puppeteer race whose evolutionary strategy is to avoid risk at all costs are petrified of the implications. The Kzin, an aggressive race of sentient cats have lost a war with the humans and maintain an uneasy truce. A team is assembled consisting of members from three dominant races in the galaxy (Human, Puppeteer, and Kzin) for an expedition to the Ringworld to explore its mysteries.