Bunny Brown and His Sister Sue embark on a series of whimsical adventures that capture the spirit of childhood curiosity and excitement. The story begins with Aunt Lu arriving to visit, sparking a chain of events involving lost rings, a mischievous monkey, and a series of unexpected encounters. Throughout the book, Bunny and Sue explore a variety of settings, from an empty house to a boat adrift on the water, while encountering animals like a rescue dog, a goat, and even a runaway Splash. They also have a series of adventures, including fishing trips, trolley rides, and a visit to a punch and Judy show. Along the way, they engage in playful activities such as setting up a lemonade stand, attending moving pictures, and solving small mysteries, like finding eggs. Despite their youthful exuberance, they also experience moments of sadness, like Aunt Lu feeling down, but the pair's adventures always bring a sense of joy and optimism. Through their escapades, they learn valuable lessons about friendship, resilience, and the importance of family, all while navigating the playful, imaginative world of childhood.