The much-anticipated sequel to The Mote In God's Eye (1974), which put Niven and Pournelle on the bestseller lists (more recent collaborations: The Legacy of Heorot, with Steven Barnes, 1987; Footfall, 1985). Here, some 25 years after the events of Mote--in which human explorers discovered a remarkably adaptable, and terribly dangerous, alien race, the Moties--two survivors of the expedition, Horace Hussein Bury, now a rich trader, and Kevin Renner, retired from the Imperial Space Navy to work as his pilot, become convinced that the Moties are on the verge of breaking the quarantine around their solar system, an event that would plunge the human race into a war for survival. The search for some way to prevent that disaster leads them eventually to a second visit to the Moties' system. As usual, the authors present a large cast of characters, including a few from Mote; many of the latter have matured engagingly, although the aliens are still more interesting than any of the humans. Meanwhile, there's plenty of action, from single combat to full-scale space battles, but the resolution of the plot depends on the cerebral--from the remarkable alien biology of the Moties to Bury's shrewd political bargaining. And, as always with Niven and Pournelle, this is science fiction with the emphasis on science. It is never easy to top a success on the scale of Mote, but Niven and Pournelle have given it an honest try. The result is sometimes slow-paced and talky, but few readers are likely to be disappointed. A good bet to make the Hugo ballot, as well as the bestseller lists.