The sense of mystery in the first chapter begins with the opening two paragraphs, in which Scout reveals that Jem had his arm "badly broken at the elbow." She goes on to relate that they "sometimes discussed the events leading to his accident," but she does not elaborate on this point except to say that she believed "the Ewells started it all." It is clear that the "events leading to his accident" will be the subject of the book, and we see much later that Jem's arm is broken when he is brutally attacked by Bob Ewell, out for vengeance after being humiliated by Atticus's defense of Tom Robinson (3). Scout adds to the sense of suspense and mystery by saying that they only thought about the events that led to the incident (and that comprise the plot of the book) when "enough years had gone by to enable us to look back on them." Clearly, these were traumatic times for the siblings and Atticus. Later in the chapter, Scout reveals her own sense of foreboding and mystery surrounding Boo Radley. She describes Miss Stephanie's (the "town scold") account of Boo's troubled upbringing, including an apparently violent attack on his father with a pair of scissors. However, all of that is in the past. The children view the Radley house as forbidden ground and Boo himself as a sort of ogre. Jem describes Boo to Dill in this way:
Boo was about six-and-a-half feet tall...he dined on raw squirrels and any cats he could catch...There was a long jagged scar that ran across his face; what teeth he had were yellow and rotten; his eyes popped, and he drooled most of the time (13).
On a dare, Jem actually sprints in and touches the side of the Radley house, a remarkable act of bravery. The children's fears about Boo may add to the sense of mystery, but they also make it especially ironic that it is Boo himself who saves them from the murderous rage of Bob Ewell at the end of the book. By highlighting the children's morbid fear of Boo and foreshadowing their violent encounter with Ewell, Harper Lee creates a sense of mystery in the first chapter.
The sense of mystery in the first chapter is created with the depiction of the strange old Radley place from a child's fearful point of view. Although Scout is recalling her childish fears from an adult perspective, she conveys the full sense of fear and wonder which the Radley house and its inhabitants evoked for her, Jem, and Dill as children.
Inside the house lived a malevolent phantom. People said he existed, but Jem and I
had never seen him. People said he went out at night when the moon was down, and
peeped in windows.
Thus she remembers the scraps of rumour and legend that used to float around concerning the Radleys, and at this stage offers no natural explanation; Boo is introduced as a 'malevolent phantom' rather than as the ordinary, if reclusive, human being that he really was. This technique lets the reader share the sense of mystery that so intrigued Scout and her playmates in those days. She goes on to recall how the legend provided endless material for their chiidish imaginings and little dramas which they would act out with gusto.