She's Cam Jansen--as in camera--because she has a photographic memory, a nifty endowment for the heroine of what's announced as a new mystery series. But Adler, author of Young Math books, has done some smart figuring here altogether. While Cam and friend Eric keep a watch on Eric's baby brother, the shopping-center jewelry store is robbed, a man runs away, and some customers-a baby(?)-carrying couple, two old ladies--emerge. The running man is caught, but the owner says he's not the thief. Then, however, he heads off in a different direction, and Cam and Eric, suspicious, pick up baby Howie and tail him. The apprehension of the culprits (the running man and, it turns out, the bundle-carrying couple) turns on Cam's attentiveness in a surprising direction--how did Eric keep Howie from crying? (And because she doesn't have Howie's bottle, she quick-wittedly substitutes a finger.) Natural dialogue, perky kids, and nobody made a fool of.