The Gripping Hand — Larry Niven; Jerry Pournelle

Return to the Mote, and to the universe of Kevin Renner and Horace Bury, of Rod Blaine and Sally Fowler.

There, twenty-five years have passed since humanity quarantined the mysterious aliens known as Moties within the confines of their own solar system. They have spent a quarter century analyzing and agonizing over the deadly threat posed by the only aliens mankind has ever encountered -- a race divided into distinct biological forms, each serving a different function. Master. Mediator. Engineer. Warrior. Each supremely adapted to its task, yet doomed by millions of years of evolution to an inescapable fate. For the Moties must breed -- or die.

And now the fragile wall separating them and the galaxy beyond is beginning to crumble....