This is book two of a series of five books.
After returning from Ringworld, Louis Wu sinks into addiction, becoming a “wirehead”. Living in an artificial world of euphoria created by electronic stimuli channelled directly into his brain by a special implant. Such is his life until he is kidnapped by The Hindmost, the recently deposed leader of the Pierson’s Puppeteers.
The Hindmost plans to use Louis’ help to find some sort of technology on Ringworld that will restore him to his former position of leader.
But upon arriving, they discover Ringworld is in trouble. The ring is gradually moving out of position in relation to its sun. Left unchecked Ringworld will eventually be destroyed by the very source of its energy. The only hope to save Ringworld and it’s billions of inhabitants is to correct the orbit.
To do this they must first find the control center of this massive artifact, and then learn how to operate it. But they are not the only one’s looking for it.