For decades, the spacefaring species of known space have battled over the largest artifact - and grandest prize - in the galaxy: the all-but-limitless resources and technology of the Ringworld. Now, without warning, the Ringworld has vanished, leaving behind three rival war fleets. If the fallen civilization of the Ringworld can no longer be despoiled of its secrets, the puppeteers will be forced to surrender theirs - everyone knows that they are cowards. But the crises converging upon the trillion puppeteers of the Fleet of Worlds go far beyond even the onrushing armadas.

Covert agent Sigmund Ausfaller is Earth's secret weapon, humanity's best defense against all conspiracies, real and imaginary, and all foes both human and alien. Who better than a brilliant paranoid to expose the devious plots of others?

But Sigmund may finally have met his match in Nessus, representative of the secretive Puppeteers, the elder race who wield vastly superior technologies.

Fleet of Worlds takes a closer look at Human-Puppeteer (Citizen) relations and the events leading up to Niven's first Ringworld novel. Kirsten Quinn-Kovacks is among the best and brightest of her people. She gratefully serves the gentle race that rescued her ancestors from a dying starship, gave them a world, and nurtures them still. If only the Citizens knew where Kirsten's people came from.

Golan Trevize, former councilman of the First Foundation, has chosen the future, and it is Gaia. A superorganism, Gaia is a holistic planet with a common consciousness so intensely united that every dewdrop, every pebble, every being, can speak for all - and feel for all. It is a realm in which privacy is not only undesirable, it is incomprehensible. But is it the right choice for the destiny of mankind? While Trevize feels it is, that is not enough. He must know.  

The newly liberated humans of the Fleet of Worlds and Sigmund Ausfaller, who had been transported by the Puppeteers from Earth to the Fleet, must contend not only with the sly Puppeteers but also the threat of the Pak, a very smart and utterly ruthless species who are fleeing the exploding galactic core in an armada of ships at near light speed. The Pak are headed towards the Fleet of Worlds, having destroyed entire planets in their wake.