The heat of the courtroom adds to the atmosphere of the trial.  It is so hot, in fact, that Atticus takes off his jacket, which is something his children never sees him do. He also sweats, even though "he was one of those men whose faces never perspired."  This indicates not only Atticus's hard work and anxiety concerning the trial; it also suggests the tense mood felt by everyone in the courtroom.  Mr. Raymond drinking a soft drink out of a brown paper bag, pretending he is drinking whiskey to give people something to talk about, also says something about the atmosphere of the trial. An outsider in the town, he doesn't go into the courtroom; indeed, he doesn't want to nor would his presence be welcome, for where would he sit?  He has aligned himself with the blacks in the community although he is white.  As a result, he belongs to neither community, thus showing the consequences of breaking the color line. That he drinks coke while pretending to drink whiskey signifies the pretense and artificiality of that barrier.  Mr. Raymond explains to Scout "you haven't seen enough of the world yet. You haven't seven seen this town, but all you gotta do is step back inside the courthouse" to understand the truth about both."  People inside the courtroom and outside know, even if they don't specifically say, that what is on trial is the traditional though immoral practice of racism in the south, and the atmosphere carries that tension.

Part Two of Lee's novel is almost exclusively about the trial and its tensions.  The night before the trial is to begin, Atticus guards the door, because there is a very real possibilty that a mob may try to wrest him from the prison and hang him.  Atticus' instincts are right.  During that long night, carloads of men come by and demand Attitcus hand Tom over.  Atticus refuses and Scout shames one of the men by mentioning the debt he owes to her father.

When the trial begins, the blacks are relegated to the balcony (Jem and Scout sneak in up there too, to watch). Atticus presents evidence that Tom could not possibly have held Mayella down and raped her because he has a lame arm.  Tom claims that Mayella tried to seduce him and he refused.  Atticus contends that the Ewell's have made up the story because of their shame that Mayella would have wanted to sleep with a black man.

Despite the evidence, Tom is conviced anyway, to the joy of the crowd and the sorrow of Atticus and his children.