"Rain Reign" is a children's novel by Ann M. Martin that tells the story of a young girl named Rose Howard, who has a passion for homonyms and a deep love for her dog, Rain. Rose is on the autism spectrum, and her unique perspective shapes her experiences and interactions with the world around her. The plot centers around the bond between Rose and Rain, which is tested when a storm hits their town. As Rose navigates the challenges of losing her beloved pet, the story explores themes of love, loss, and the importance of family and friendship.