An implied metaphor is used in Chapter 25 when Scout reflects on Tom Robinson's death and the inevitable failure of Atticus' attempt to see Tom gain justice. After hearing about Tom's death and how his wife responded to hearing the news, Scout reports what other people think and say about the event in Maycomb, and it is clear that the prejudice against Tom because of the colour of his skin is what drives the negative comments in these reports. Scout reflects on the situation and concludes the following:
Atticus had used every tool available to free men to save Tom Robinson, but in the secret courts of men's hearts Atticus had no escape.
Note the two metaphors that are used here. Firstly, Atticus used "tools," which refers to the various legal processes and rhetorical strategies that he used to try and encourage the jury to respond to Tom's case honestly and truthfully. Secondly, Scout says that "in the secret courts of men's hearts," likening the heart of man to a courtroom which is "secret" because so much that goes on in these secret courts are decided by prejudices and beliefs that we may have little awareness of.