"The Mystery of the Missing Cat" is a children's book about Aspen, a young detective who is determined to find her neighbor's missing cat, Mr. Whiskers. Aspen sets out to gather clues and interview suspects, discovering that a shifty pet thief has been stealing pets in the neighborhood, including Mr. Whiskers. Aspen and her friends organize a rescue mission and catch the pet thief, rescuing all the missing pets. Aspen becomes a hero in the neighborhood and continues to solve mysteries. The book emphasizes the importance of friendship, bravery, and problem-solving skills.