Tully and Kate's friendship begins in the era of bell bottoms and bohemian free spirits, meeting on Firefly Lane as teenagers. Even though Tully and Kate are neighbors attending the same school, their lives couldn't be more different: Kate grew up in a stable family home with casseroles and TV nights, while Tully grew up with an off-and-on hippie mom named Cloud who is usually high, and lets her eat all the junk food she wants. Tully is popular and rebellious, noticed by everyone even though she acts like she doesn't care, while Kate is insecure and bullied on the bus. Even though the two are total opposites, Tully sees Kate as deeply kind and special, while Kate sees Tully as everything she wishes she was.
During the first decade of their friendship, tons of events occur that will mark the rest of Tully and Kate's very different lives. Tully catches Kate's brother kissing another boy, keeping his secret, and later, is raped by a popular boy from school named Pat (which then leads to a pregnancy scare). Kate is Tully's shoulder to cry on, punching a girl and almost running over Pat in defense of her friend, and she has a few issues of her own: she has a panic attack while getting high with Tully in a field, and she catches her mom cheating on her dad in the living room. The two fight at some points, such as when Kate finds out Tully lied about her mom having cancer, but they quickly reconcile — in this decade, they are inseparable.