Adam Parson goes on a morning hike with his son, Eugene, and the boy returns home alone. Eugene is autistic and nonverbal, so he can't explain what happened. This is how Angie Kim sets up Happiness Falls, which chronicles how the Korean-American family tries to make sense of Adam's disappearance. Kim tells NPR's Scott Simon about the complicated relationship between Eugene and his siblings, and why she wanted to emphasize that a lack of verbal communication does not equal a lack of thought and feeling.