On the eve of her 16th birthday, high school sophomore Samantha Baker is plagued with the typical teenage concerns about boys, school dances, and the ever-awkward physical and social changes that come with being a teenager. However, her excitement about her milestone birthday quickly turns to disappointment when her entire family forgets the occasion due to her older sister's forthcoming wedding, which has consumed all of their attention. Feeling invisible and neglected, Samantha's day spirals further downward as she pines for her crush, the popular senior Jake Ryan, while simultaneously being tormented by a relentless freshman geek who won't take a hint.

Amidst the chaos of her sister's wedding preparations and the high school dance, Samantha navigates a series of embarrassing interactions and misunderstandings. She grapples with her feelings of insignificance at home, the social hierarchy of high school, and her own self-worth. Meanwhile, Jake, the object of her affection, begins to take notice of her after finding a misplaced personal note, leading to his own revelations about what he wants versus the expectations of his social circle. As the day unfolds, Samantha comes to realize that turning 16 isn't exactly the dreamlike turning point she anticipated, as her life becomes a bittersweet symphony of adolescent woes and small victories.