Stella McKinney has a great life. With a Malibu beach house, doting husband, and a flourishing business, everything is coming up roses—until it isn't. When her beloved husband Grant begins behaving out of character and devoting more time to his career, Stella has reason to question his fidelity for the first time in their marriage. As Stella's quest for the truth morphs into a sick obsession, the last thing she expects is a perfect stranger to show up at her door, a beautiful woman who knows intimate details about Stella and Grant that no one else could possibly know. With her marriage and idyllic lifestyle at stake, the only way to uncover the truth is to ask herself how well she really knows her husband—and ultimately, how well she knows herself. And as Stella discovers, sometimes the truth is downright terrifying.