"Wait Till Helen Comes" is a children's novel by Mary Downing Hahn that tells the story of a young girl named Molly and her family. They move into an old house near a graveyard, where Molly's new stepmother, Diana, hopes to create a happy home. However, Molly's life takes a turn when her younger brother, Michael, befriends a ghost named Helen, who has a mysterious and tragic past. As the story unfolds, Molly becomes increasingly concerned about Helen's influence on Michael. The ghost's presence leads to eerie events and challenges the family's dynamics. Ultimately, Molly must confront her fears and protect her brother from the dangers that Helen represents.