Karen M. McManus is an American author best known for her young adult mystery novels. She was born in 1977 and grew up in Massachusetts. After earning a degree in English from the College of the Holy Cross, she went on to work in publishing and marketing. Her debut novel, "One of Us Is Lying", was published in 2017 and became a New York Times bestseller. She has since written several other popular YA mystery novels, including "Two Can Keep a Secret" and "The Cousins". McManus is known for her gripping plots, well-drawn characters, and suspenseful writing style.