Mariana Ruiz is bringing a lot home from her vacation in Puerto Rico, including memories of a hot summer romance, a new understanding of her cousin Lilly Sanchez who's enrolling in Mariana's suburban Philadelphia high school.

Mariana's best friends, Madison and Emily, aren't thrilled about the new arrival, especially when Lilly soars through the ranks of Spring Mills High's social circles. But Mariana has other things on her mind. Like Mariana's developing crush on her locker buddy, Bobby, the one boy to ever take Emily on a real date. But it's the revelations at Mariana's Sweet 16 party that make it clear that life at Spring Mills High School will never be the same again.