It's summer, and the Weird Sisters are convinced that the residents of Covenly aren't coming to their pet emporium's and newly opened detective agency's because the sisters are too strange. So they decide to let nine-year-old Jessica Nibley teach them how to play on the swing to fit in. They soon discover the town's beloved tire swing lying on the ground with its rope severed. Who would do such a thing? And why? Jessica and the sisters are determined to solve the mystery. As they search for clues, they stumble onto a second mystery: the robin that nests at Chelsea Oh's house has gone missing. So they plan to find both the robin and the swing vandal.