Riley is a lively girl. In his mind, five characters, joy, sadness, fear, disgust and anger, influence his way of doing. As he grows, his experiences become memories, filed in colored spheres. Its five most important "fundamental memories" take the form of floating islands. Joy acts as a leader and tries to keep sadness aside. At the age of 11, Riley moved with her parents to San Francisco for her father's new job. The new house, however, is old and cramped, the local pizzeria serves only broccoli and his father is stressed out by his job. When sadness begins to touch Riley's happy memories, making them sad, Joy tries to protect them by isolating her. On Riley's first day at her new school, Sadness makes Riley cry in front of her classroom, creating Riley's first sad memory. Joy tries to eliminate it, but accidentally drops other fundamental memories during a struggle with sadness...