Change isn't anything new to Riley Andersen. When she was eleven years old, she and her parents moved across the country from Minnesota to San Francisco. But through it all, Riley's Emotions—Joy, Sadness, Anger, Disgust, and Fear—guided and supported her.

Now Riley is thirteen years old, and her Emotions can't wait to see what her teenage years will bring. But the idea of starting high school elicits all kinds of feelings, including four new Emotions! Anxiety, Envy, Embarrassment, and Ennui enter Headquarters, ready to help Riley succeed in high school. Joy and the core Emotions aren't sure about these newcomers and how much they're changing Riley; the new Emotions think it's time to take a different approach now that she's a teenager. Although change happens to everyone—and especially to Riley—this chaos both inside and outside of Headquarters is unlike anything Riley and her Emotions have experienced before!