"Ralph S. Mouse" is a children's book written by Beverly Cleary. It tells the story of a small mouse named Ralph who lives in a motel and has a special ability to communicate with humans. Ralph's adventures begin when he befriends a young boy named Keith, who helps him navigate the challenges of living in a human world. Throughout the story, Ralph experiences various escapades, including riding a toy motorcycle and dealing with the dangers of being a mouse in a busy environment. The book highlights themes of friendship, bravery, and the importance of believing in oneself, making it a beloved classic for young readers.