"A Stranger Is Watching" is a suspenseful novel by Mary Higgins Clark that revolves around a young girl named Kathy who witnesses a brutal crime. The story unfolds as she becomes a key witness in a murder trial, putting her life in danger as the killer seeks revenge. As the plot progresses, Kathy and her mother face increasing threats, leading to a tense race against time. The narrative explores themes of fear, justice, and the impact of crime on innocent lives, keeping readers engaged with its twists and turns until the very end.