A neat, involving mystery adventure--despite the fact that readers will spot the culprit straight off, whereas Ben, the alert young hero of Funny Bananas, doesn't catch on until the end. It takes place on an Arizona dig run by a family friend, Ben's ""Aunt"" Celie. New Yorker Ben is there for Christmas vacation, hoping to photograph some wild animals and keep his pet coatimundi, Frito, out of trouble. But while he is off in the desert taking pictures, Ben notices a car spying on the camp and a plastic bag of pottery shards buried near its tire tracks. Though men at the camp dismiss the shards as the abandoned loot of small-time pot robbers, Ben suspects a big-time plot when he overhears a tough character in a flame-painted truck talking on CB to someone at the dig. ""Get rid of the kid,"" the man says ominously . . . and then Ben's tent is infested with rare and deadly scorpions. The archaeologists are lured sway by a fake site, and Ben and Frito return from an outing to face and hold off a gang of robbers. . . until the others separately converge for the roundup, bang-up ending. Less frenzied than Funny Bananas and no edge-of-the-chair thriller, this has an adequate built-in suspense level and a solid sense of life on a deserg dig--which makes, not incidentally, a dandy closed-cast crime-mystery setting.