Who is Sarah McGinniss from The Midnight Club and what is their importance?

Sarah McGinniss is an author, who is currently writing a book entitles, The Club, a novel about organized crime bosses. Over the course of the novel, Sarah finds herself in the middle of a murder investigation. Her work also leads to the kidnapping of her son. In the end, Sarah turns over all the information she has gathered to insure her child's safe return.