Riley MacPherson is a fictional character from the novel "The Last Thing I Told You" by Emily Arsenault. She is portrayed as a young woman navigating the complexities of her life and relationships, particularly after a significant event that impacts her family. In the story, Riley's journey involves uncovering secrets and confronting her past. The narrative explores themes of loss, identity, and the bonds of family, making her a relatable character for readers who appreciate emotional depth in literature.