Montana and her sister, Arizona, are named after the mountainous states their mother left them for. But Montana is a New York City girl through and through, and as the city heats up, she's stepping into the most intense summer of her life. With Arizona wrapped up in her college world and their father distracted by yet another divorce, Montana's been immersing herself in an intoxicating new friendship with a girl from her acting class. Karissa, 23 to Montana's 17, is bold, imperfectly beautiful, and unafraid of being vulnerable. She's everything Montana would like to become. But the friendship with Karissa is driving a wedge between Montana and her sister, and the more of her own secrets Karissa reveals, the more Montana has to wonder if Karissa's someone she can really trust. In the midst of her uncertainty, Montana finds a heady distraction in Bernardo. He's serious and spontaneous, and he looks at Montana in the way she wants to be seen. For the first time, Montana understands how you can become both lost and found in somebody else. But when that love becomes everything, where does it leave the rest of her imperfect life?