Vernor Vinge's 1999 sf novel A Deepness in the Sky is a prequel to his 1993 tour de force A Fire Upon the Deep. It's a plot-driven romp reminiscent of Keith Laumer at his best (though without Laumer's tongue-in-cheek humor) and Hal Clement (though with less of a physical-science foundation). The aliens are entertainingly different, though not terribly "alien" in their psychology. The big theme—the evil of slavery—echoes Richard Adams's Shardik. Thoughtful, readable, distractingly improbable ... and far too much hang-by-a-thread save-the-universe by luck to be fully satisfying. But nevertheless, a fun read.