Lewis Dodge, almost 12, is invited to go on a camping trip to Yellowstone Park with his new neighbors, the Rupes, and their 12-year-old son, Harry. Lewis's twin sister, Alison, is also asked along to help take care of the Rupes' two younger children, Billy and Ariadne. At first the Dodge kids are excited by the prospect of nine days with the Rupes' lax rules -- all the junk food and videos they can consume -- but they soon realize that the trip will not be ideal. The Rupes are all spoiled; they think money can buy amusement, or atone for rudeness and neglect. (The Rupes don't even know that Billy is seriously nearsighted until Lewis tells them.) As Alison slavishly watches the children, Lewis comes upon a mystery: Two men have been following the Rupes' trailer since it left Washington State. When Billy finds a $100 bill in the trailer, Lewis thinks he knows what's going on. One night the two men come looking for their stash. But instead of finding their money, they find the five children, kidnap them, and head toward the Canadian border. Because of the kids' ingenuity, however, they are foiled before they can leave Montana. The elder Rupes really are terrible, but the Dodge siblings come out of this diverting caper intact. The morals about the evils of lenient parenting aren't subtle, but Roberts (Caught, p. 563, etc.) delivers them well.