Karl, who is mentally retarded, is released from a psychiatric hospital (which he refers to as a nervous hospital) where he has been hospitalized since the age of 12 for the murder of his mother and her lover, Jesse Dixon. He returns to his childhood town in Arkansas and obtains a job repairing small motors at Bill Cox's repair shop. Karl befriends a young boy, Frank (Lucas Black), and is soon invited by Frank's mother, Linda, to move into the family's garage.
As a strong relationship develops between Karl and Frank, a confrontation builds with Linda's abusive boyfriend Doyle (Dwight Yoakam). Karl eventually kills Doyle with a lawnmower blade to protect Frank and his mother, out of his love for them. After he murders Doyle, he is sent back to the institution.