What happens to Scout and Jem on the way home from the school pageant? What does the incident reveal about Boo Radley?

Scout and Jem are attacked on their way home from the pageant. They are attacked by Mr. Ewell. Unfortunately Atticus was slightly mistaken about Bob. Given enough alcohol, Bob would take his vengeance out on children. Fortunately the neighbourhood "monster" was actually the children's guardian angel. Boo was making sure Scout and Jem got home okay and intervened when Ewell attacked the kids.