Katrina Hollister, her twin sister Kiara, and their quirky group of pre-teen friends find themselves playing spy during their summer vacation in the prestigious gated community of Sinclair Estates.

Not only does Katrina and her crew investigate why ginormous mushrooms are randomly appearing then disappearing when their strange new neighbor is about, but she must also deal with the up-and-coming teen sensation who moved in across the street and stole her crush. To make things worse, her mother starts dating her crush's gorgeous father—all of which she must stop.