In this third of a series, strange goings-on at the local fair have Laura, Jeffrey and Jeffrey's invisible friend, Bradford, puzzled--but not for long. When two races are won by cheating, when Laura buys a raffle ticket that has neither prize nor drawing-time on it, when the three discover a box of disguises, it's plain that something's afoot, With the help of Bradford (at 210 years old, a world-class case of arrested development), the pie-eating contest becomes a wild pie-throwing event, and a pair of young hustlers confess. Bradford combines all the worst features of a younger brother, and, as in his previous ""appearances,"" he creates instant havoc wherever he goes. Black- and-white drawings, mostly of adults discomfited by Bradford's antics, accompany an easy text. Fans of Adler's Cam Jansen hooks--especially Cam Jansen and the Mystery of the Carnival Prize (Viking, 1984), which has a similar plot--will enjoy this.