Ellie Mack is a fictional character from the novel "All the Missing Girls" by Megan Miranda. She is a young woman who goes missing, prompting a complex investigation that unfolds over several days. The story is told in reverse chronological order, revealing the events leading up to her disappearance. The narrative explores themes of memory, relationships, and the impact of secrets on a community. Ellie’s case intertwines with the lives of other characters, including her friends and family, as they grapple with the mystery surrounding her absence and the truths that emerge throughout the story.