Wrap-up of the far-future trilogy (Juggler of Worlds, 2008, etc.) set 200 years before the discovery of Niven's ever-popular Ringworld.
The cowardly, herd-minded Puppeteers discover that a gigantic black hole at the center of the galaxy threatens to engulf all life. So they flee, launching entire planets across the void. The ferocious, single-minded Pak are also fleeing the core explosion, plundering and destroying as they go. Paranoid genius Sigmund Ausfaller, originally from Earth, has contacted another developing civilization. The Gw'oth aren't that smart individually, but they can form superintelligent mind-melds of up to 16 individuals. Er'o, one of the components of the 16-plex Ol't'ro, agrees to help Sigmund investigate the Pak. Intriguingly, humans and Pak turn out to be related—not that it matters in a universe where no species trusts any other. Individual characters aren't particularly convincing, but the depth of the various species’ backgrounds and motivations more than compensate. Sigmund's problem: How to persuade the pusillanimous Puppeteers to take action against the rapacious Pak while allowing the supersmart Ol't'ro to help?
Old-fashioned cerebral science fiction, with a huge array of fascinating aliens, subtle interactions between them and knotty problems for them to solve.