The protagonist Riley moves with her family to San Francisco due to her father's job, preparing to adapt to the new environment. However, just at this time, the two brain ministers Joy and Sadness, who control happiness and sorrow in Riley's mind, get lost in the vast expanse of her consciousness. With only Anger, Fear, and Disgust left in charge at headquarters, the once optimistic Riley turns into a cynical teenager. Joy and Sadness must find their way back through the complex world of the mind to headquarters as quickly as possible, so Riley can regain her original happy and normal emotions...