What persuades the lynching party to give up their attempt on Tom's life in Chapter 15 of To Kill a Mockinbird?

This scene is one of the most heart-wrenching and emotional ones in the entire novel: Scout shows up at the prison steps, and speaks with Mr. Cunningham about his son, Walter, with whom she attends school. In fact, early on in the novel, Walter joins the Finches for dinner and drowns his food in syrup. This leads to Scout's life lesson from Calpurnia, where she is told not to place her self above her company, even if they are poor.

This prior experience with Walter Cunningham becomes invaulable as Scout relates to Mr. Cunningham, and turns an entire angry lych mob into a group of soft-hearted daddies and husbands. The black-and-white movie version of the novel does this scene, in particular, great justice.