Tessa Young is an 18 year old college student with a simple life, excellent grades, and a sweet boyfriend. She always has things planned out ahead of time, until she meets a rude boy named Hardin, with too many tattoos and piercings who shatters her plans.

Rylee Devine is the little sister of One directions drummer Josh Devine. After an accident resulting in a loss of her parents, she is taken in by her brother and the band. As the spend the summer together, one of the boys finds himself falling for her, but will he break the 'Sister Rule' even if it means risking a friendship?