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.