It is in the second part of chapter 15 when Atticus Finch goes to the town's jailhouse to stand guard for Tom Robinson's protection. Atticus had received word that, even though he is behind bars, Tom is far from safe. A lynch mob is likely coming for him that night.

There are many good quotes that you could select from to help illustrate this tense episode from the book. Consider the following.

The description of the jailhouse itself is noteworthy. It paints the picture of the building as austere and formidable. It is clearly not an inviting place—it is a jail after all. This short description helps set the mood for the events to follow:

Starkly out of place in a town of square-faced stores and steep-roofed houses, the Maycomb jailhouse was a miniature Gothic joke one cell wide and two cells high, complete with tiny battlements and flying buttresses.

We see the tension really start to build soon after. It is Atticus's subtle yet deliberate response to an incoming threat that shows us exactly why he is visibly sitting outside the jailhouse in the middle of the night and how he is a man who keeps his cool:

We saw Atticus look up from his newspaper. He closed it, folded it deliberately, dropped it in his lap and pushed his hat to the back of his head. He seemed to be expecting them.

Although it does not happen exactly how she intends it to, Scout is able to diffuse the potentially dangerous situation that occurs next. After attempting to make small talk with Mr. Cunningham, the man decides to call off their plans for lynching Tom Robinson. The following quotation could illustrate that the situation has been temporarily resolved:

As they had come, in ones and twos the men shuffled back to their ramshackle cars. Doors slammed, engines coughed, and they were gone.