When Jem and Scout are brought back to the house in Harper Lee's To Kill a Mockingbird, the doctor sees to Jem's broken arm. (Jem will not regain consciousness until the next day.)
At the end of chapter twenty-nine, Scout has realized that Boo Radley is in Jem's room, in the shadows. At the beginning of chapter thirty, the doctor shoos everyone out, and Atticus, seeming to know that the lights would be difficult for Boo, takes the group onto the front porch where Boo can sit in the dark, rather than sitting in the living room.
Heck Tate (the sheriff) and Atticus have a serious argument. Atticus believes that Jem killed Bob Ewell when he attacked the children. Heck Tate insists that Ewell fell on his own knife. Atticus argues that this is not the truth, and refuses to lie to protect his son, knowing that if he does so, his children will lose faith in him for lying. Atticus stresses to Heck Tate that Jem and Scout are all he has in the world.
Heck Tate insists that this is the story they will release, but then unexpectedly points out to Atticus that he is not trying to save Jem: there was no way Jem could have killed Ewell, with a broken arm. Heck Tate insists that a private citizen should not be punished for stopping a crime. Without a fuss, Atticus finally understands that Heck Tate is speaking of Boo Radley—who killed the man responsible for the needless death of another man (Tom Robinson), and who tried to kill Atticus' kids. The sheriff goes on to say that should the news get out, no one would leave Boo alone for the heroism he had displayed. Heck knows that this would be an injustice for the gentle and solitary man who has been locked away from the companionship of society for so many years.
Heck Tate leaves, and Atticus repeats the "official cause of death" to Scout: Bob Ewell fell on his knife. When Atticus asks Scout if she understands, she puts it quite simply: to do otherwise would be like killing a mockingbird—something that never hurts anyone else, never does any harm.
Atticus and Scout realize that Boo Radley saved the children's lives from the attack of Bob Ewell.
In Chapter 29 of Harper Lee's To Kill a Mockingbird, the sherriff, Atticus, the doctor, and Scout discuss what has transpired this night; only afterwards, does Scout notice the hollow-eyed Arthur standing in the corner. Chapter 30 begins with Atticus, gentleman that he is, introducing his daughter to Arthur Radley as they stand in Jem's bedroom. Then, Atticus suggests that they all go out on the porch as it is still warm and there are plenty of seats. Scout wonders why Atticus has not suggested that everyone go into the living room instead, but "then I understood. The livingroom lights were awfully strong." Like her father, Scout realizes that Boo Radley would feel safer and more comfortable in the shadows of the porch and in the dark of the outdoors. After all, Scout has discovered him in a shadow against a wall of Jem's room.
In a second incident of understanding, Scout runs to her father at the end of his discussion with Sherriff Tate about how to resolve the death of Bob Ewell. Instinctively realizing that Scout understands, Atticus places his face in her hair and rubs it after Scout commiserates with him upon the necessity of preventing harm from the mockingbird, Arthur Radley.
"Scout," he said, "Mr. Ewell fell on his knife. "Can you possibly understand?"
"Yes sir, I understand," I reasusured him. "Mr. Tate was right."