When his best friend Kyle moves to ``stupid-Cleveland- stupid-Ohio,'' a disgusted Willie expects the girl who moves in next door to have a closet full of party dresses, a unicorn with a lavender tail, and a bike with hearts and sparkles. Determined to know the worst, he sets out to spy on her, cheered on, long distance, by Kyle—only to have Lily glare back through his periscope and pull down her shade. Meanwhile, mysterious other children are seen next door and there's an outstanding new player on the opposing Little League team. To Willie's surprise (though not, probably, the reader's), these all turn out to be Lily, whose possessions—including a costume box—would be appropriate for any boy, and who enjoys sleuthing as much as Willie does. Joosse catches the kids' concerns with engaging humor; her realistic dialogue and approachable, staccato style—plus Truesdell's wonderfully lively and comical b&w illustrations—are sure to appeal. (Fiction/Young reader. 7-10)