Coming from an overseas posting, Rianne, Shannon, and Abe find their new neighborhood--a plastic community a stone's throw from the State Department, where their father is chief of security--impossibly stodgy. Then they meet an ordinary-looking opossum who talks and gives away luck that's quite real, as Rianne learns when she buys a winning lottery ticket. Unfortunately, the good luck is always countered by bad--a scary automobile accident, a tree falling through the roof; when the bad luck escalates to having their father taken hostage by terrorists, the kids swear off further opossum meddling. After all, the animal couldn't even save her own woods from destruction. So much doesn't add up here that the book doesn't quite make it as humor or suspense: e.g., though the opossum talks, she insists on dumb-animal status; and the bad luck is far out of proportion to the good. The moral seems to be either: Don't mess with Mother Nature, or press your luck--or make bad puns like ""impossumble.