In the seventh book of the Calendar Mysteries -- an early chapter book mystery series featuring the younger siblings of the A to Z Mysteries detectives -- the kids and their pets are going to march in the Fourth of July Pet Parade! The winner of the patriotic pet costume contest gets a great prize -- to be mayor for a day! For Bradley's entry, Polly the Pony gets to be President Thomas Jefferson for the day. But Polly runs off with her red wig and hat still sitting on her head. Maybe she has stage fright! Can the kids find her and calm her down before the fourth of July festivities begin?