The story continues to advance within these chapters, and things are beginning to get very interesting. By the twelfth chapter, it becomes clear that Jem is no longer a kid - not only does it look like he's going through puberty, but multiple times throughout the chapters, he shows an extreme maturity in his decisions. He seems to possess to greater understand the gravity of things that are occurring than he did in previous chapters, and he also understands a certain wrongness of what is happening - he stands beside his father proudly when the flash mob forms, unwilling to run, even after Atticus tells him to. His speech also reflects this change - he uses an extended vocabulary, along with grammar altered by education.
Though less so, Scout has also changed. Though her personality has not changed as of yet, her ideas have - she now grasps the world around her with more understanding, gained not only from education but fro experiences with her father and brother. Though she is still naive enough that she does not quite understand some of the thing discussed in the courtroom, she is beginning to understand some of the ideas presented in this book - most fluently, the idea of racism.
But the most important part of the chapters is the trial. Through it, the reader begins to understand what really happened. Though the Ewell's story is that Tom Robinson raped Maybella Ewell, the true details emerge as Atticus picks apart the case: that Tom Robinson and Mabella Ewell are both victims.
To Robinson had been doing favours for the Ewells for quite a while - tending their lawn, cleaning their yard, caring for their flowers, etc. However, on the day in question, Maybella Ewell was alone in the house - the children were out, and her father was off at the pub. She invited Tom inside, and the predictable happens - Maybella reveals her affection for Tom, and the two begin to kiss. However, at this point, Mr. Ewell staggered home, drunk, and saw the two kissing through the window. Outraged, he chases Tom out and then beats his daughter savagely, threatening her into silence.
Though the case is solid, there is only one way this could go - in a town such as Maycomb, a man such as Tom Robinson could never win a case, even against a drunkard such as Robert Ewell.
This picture best represents these chapters in my eyes. "Justice is blind" is a common adage of the legal system, harkening to an unspoken goal of equal representation under the law, regardless of group. However, this is not so in real life or in the book - people are biased, and regardless of how we work against it, some will always fare better than others in the court of law. This is sadly true in To Kill a Mockingbird - though Atticus is good lawyer, and Ewell's story is full of holes, Tom Robinson will not win the trial, simply because of the colour of his skin.