The fourth and final book in the Investigators of the Unknown series turns intriguingly on the way ""people never seem to like each other in equal amounts."" Poco (who talks to animals) loves a robin who cares only for Juliette, the old cat who used to belong to their neighbor, Angela, whisked away to Mexico for a year by her high-powered parents. Georgina, the scientific one, misses her terribly, but when Angela returns, unrecognizably tall and aloof, she rebuffs Georgina as if she ""were a small, bothersome gnat."" Are the disturbing changes in Angela caused by her own lopsided longing for a distant mother, or has she been abducted by aliens in transparent flying marbles? Angela later vanishes and claims an alien kidnapping (or did she just mn away?), and Juliette passes on to another world, maybe in more ways than one. Lisle (A Message from the Match Girl, 1995, etc.) gives readers so much to ponder that those seeking a UFO encounter will be easily distracted by the more intricate trappings of human intercourse. A thoughtful, resonantly written puzzle.