Following the flawed but outstanding Against Infinity (p. 145), Benford arrives with another expert hard-science sf novel--a sequel to the rather unfocused and labored In the Ocean of Night (1977). There's a fascinating double-narrative thread here. Aliens called ""Swarmers,"" together with their intelligent adult form, the ""Skimmers,"" have been dumped in Earth's oceans by invading machine-aliens in the hope that they and the humans will destroy each other. And shipwreck survivor Warren drifts on a raft in the Pacific, painfully attempting to communicate with the Skimmers (who aren't hostile and understand the situation), while a confused, panicky human race edges toward nuclear war. Meanwhile, in the book's other plot-strand, starship Lancer, exploring nearby stars, has found only pitiful remnants of once-advanced cultures and technologies. Around each planet where life has arisen orbits a Watcher, an artificial asteroid left by the same machine-aliens, whose function is to exterminate organic life. (A million years ago Earth's Watcher was destroyed by a friendly spaceship.) And trying to make sense of all this on Lancer is wise old polymath Nigel Walmsley--but even he can't dissuade his shipmates from making a disastrous attack on a Watcher, which retaliates murderously. . . leaving the ship stranded light-years from warring Earth. The characters are solid; the alien planets and creatures, built on brilliant scientific extrapolation, are utterly convincing; the taut, gripping narrative is marred only by overlong experimental passages. In sum: another splendid performance that will have readers on the edge of their seats--waiting for the trilogy's concluding volume.