Describe events prior to the scene at the Maycomb jail that show the tension and unrest of town in To Kill a Mockingbird.

In addition to the incidents clairewait points out, the
incident at the beginning of Chapter 15 (prior to the scene outside the jail) is a good
indicator of tension and unrest in the town. 

After dinner,
Jem answers a knock at the door, and tells Atticus that Heck Tate is there to see him. 
When Atticus tells Jem to invite Heck in, Jem reports that there are other men with him
and that Atticus should go outside.  Though the children only hear bits and pieces of
the conversation, they understand that the men are discussing the Tom Robinson trial and
gather that the men are warning Atticus of trouble. 

Scout,
who notes that "In Maycomb, grown men stood outside int he front yard for only two
reasons: death and politics," wonders who has died; unlike Jem, she is unable to
understand the scope of the situation.  As the men get closer to Atticus, Jem screams
that the phone is ringing, because he senses trouble.  The men laugh, and eventually
depart, but Jem, who has been watching intently, says to Atticus, "They were after you,
weren't they?  They wanted to get you, didn't they?"  Atticus replies by telling Jem
that those men were friends.  Still, it is clear that Jem understands the tension of the
situation.