Riley, a young girl, is uprooted from her life in the Midwest when her dad gets a job in San Fransisco. She needs her emotions to guide her through her new school, new people, and new life. But, an accident involving Riley's happy memories changes her entire outlook. Joy and Sadness need to find her memories and return them from the Headquarters before its too late.
Riley leads a pretty good life, with her loving parents, participation in hockey and love for Minnesota, her home state, with the help of her emotions; joy, fear, sadness, disgust, and anger. But when she moves to San Fransisco, joy and sadness disappear, symbolizing her difficulty accepting her new life. Joy and Sadness go on a quest to return home and save Riley.
All of us have various brain functions that govern our response to various situations. The functions responsible for Happiness, Sadness, Fear, Anger and Disgust are characterized and the details of the activities they do to run the life of a young Girl Riley right from her birth is what drives the story. When a sudden change in the life or Riley upsets their rhythm, they try to control the situation too much, which creates more confusion for Riley. Their adventures in an attempt to restore normalcy is what forms the crux of this movie.