Willy, a very rational boy, is forced to grapple with his unpredictable emotions on an adventure with a classmate. On a journey through a nearby forbidden forest, he discovers nine primary emotions that put him in hazardous situations, then help him overcome them. Each emotion appears in the form of a colorful light. On his way to school, he meets his first emotion, Happi, and soon after Wonder drags him into the forest. He struggles with Panicky after getting scared by something following him, but his pursuer ends up being his classmate Mia, who was trying to make sure he was safe. Because Mia scared him so badly, Willy unleashes his darkest emotion Fury, and he verbally attacks Mia for scaring him, demanding that she leave him alone. But after she leaves, Shame and Melancholy visit Willy, and he regrets that he was so mean to Mia. He decides to stand up to his emotions and selflessly focuses on finding Mia. Courage appears as Willy tries to make things right, and even though Willy gets physically harmed during his search for Mia, he still manages to find her. She had tripped and fallen over a cliff and is clinging to life by her fingertips curled around a tree root. Willy tries to rescue her but accidently lets her fall. His assumption of her death hits him hard, and he feels an unbearable pain in his heart. However, Mia hadn't fallen the whole way down but onto a ledge a little farther down from the surface. Willy uses Fury, Lovely, and Courage to find the strength and brevity to pull her up. While trying to find a way out of the forest, they come across a mysterious old man playing the violin who lives in a nearby cabin. At first, doubting the intentions of the old man, they pretend they are not lost. Shortly after knowing more about him, they become friends, and the old man takes them to his cabin for some water and to wrap Willy's wounds. In the meantime, he mentors them on emotions and promises to direct them back to their school. However, on the way back, the old man takes them on a detour. He takes them to an old factory that leaked poison and destroyed the nearby environment and wildlife. These horrible surroundings cause Willy to meet his most repelling emotion: Disgusty. The old man gives them a vital lesson about the environment by connecting basic human behavior and emotions. When they finally get back to school, they find a bunch of people looking for them. Willy's father furiously blames the old man for all the trouble and pushes him to the ground. Lying on the ground with his broken violin, the old man does nothing but show empathy. He then departs back to his cabin. By the end of this coming-of-age story, Willy has changed into someone who cares much more about his emotions and has more control over them.