Born to teenaged parents in a small town, sixteen-year-old Lucy Diamond (Sarah Bolger) longs for a traditional family, but with an immature working mother (Claire Danes) and a strict, frequently absent father (James Marsden) she is mostly on her own. As she senses her parents' emotional distance, Lucy grows close to her childhood best friend, Kevin (Thomas Mann), who soon becomes her first sexual partner. After he abruptly moves away, Lucy struggles to make sense of her fledgling sex life, plan for her future, and help her mother start over again.