Karl Childers, a man with an intellectual disability, has spent most of his life in a mental institution after committing a violent crime in his youth. After being deemed no longer a threat to society, he is released and returns to his small hometown in Arkansas. Trying to reintegrate into society, Karl finds solace in fixing small engines and takes up residence in the garage of a local repair shop. He develops a friendship with a young boy named Frank Wheatley and his kind-hearted mother, Linda. As Karl bonds with Frank, he begins to experience a sense of belonging and purpose for the first time, despite his troubled past.

However, the tranquility of their lives is threatened by Linda's abusive boyfriend, Doyle Hargraves, whose volatile behavior creates an atmosphere of fear and tension. Karl's loyalty to his new friends and his growing protective instincts force him to confront the darker aspects of his past and the present dangers around him. As he strives to maintain the fragile peace he has found, Karl faces crucial decisions that will test his moral compass and the strength of his resolve.