The film’s real protagonist is Joy (voiced by an effervescent Amy Poehler), one of five emotions who steer Riley through life via a control center in her mind that’s akin to the bridge from the Starship Enterprise. Joy and her cohorts — including Fear (Bill Hader), Disgust (Mindy Kaling), Anger (Lewis Black), and Sadness (Phyllis Smith) — all work together to keep Riley emotionally balanced, and for the first 11 years of her life, the primary influencer is Joy, as evidenced by Riley’s sunny demeanor.
But as adolescence sets in, Joy finds her lead role usurped. Suddenly, Sadness wants to pipe in at inappropriate times — coaxing Riley to cry during her first day at a new school, for instance — and as the two emotions jostle for control, both of them fall into the deepest reaches of Riley’s mind and have to work their way back. Meanwhile, left to their own devices, Fear, Disgust, and Anger collude to transform Riley into a moody preteen.”