The Moat Around Murcheson's Eye

There, 25 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.