In a prologue, high school freshmen Annie, Marisa, and Kelly vow to open their college acceptance letters together at their senior bash.

In class, Annie sees Kelly and the other popular girls laughing about something, causing her to have a panic attack and run to the bathroom.

Marisa goes to comfort her, but Kelly follows them and pushes her outside, where they get caught by the annoying hall monitor, Andy, who gives them both detention.

Marisa and Annie decide to skip class for the rest of the day and go on adventures while trying to discover the location of the senior party.

Annie sees Kelly and her popular friends getting into a limo to go to the senior party; she gets depressed and eats an entire bag of potato chips.

After the party, Annie, Marisa, and Kelly finally honor the promise they made four years ago and open the letters together.

In December 2015, it was announced Jennette McCurdy, Kiersey Clemons and Virginia Gardner would lead the ensemble cast in the film, with Nick Kreiss making his directorial debut from his own original screenplay.