The turning point is basically like the climax when T. J. Avery becomes involved in a robbery and assault with two white boys he considers friends. The boys go too far, and when T. J. tries to get out of it, he is beaten up by his so-called "friends" , who wear masks to conceal their identity.  The blame for the robbery falls onto T. J.causing a group of angry white men to attack the  Avery house intent on hanging T. J.  David Logan, Cassie's father, determined to stop them, sets his own cotton on fire to distract the landowners and prevent the hanging.

I would say a major turning point is when black and white people work together to put out the fire. The whites, of course, are the same people who had threated the lives and businesses of the blacks, but under these dire circumstances, they come together for the common good of the community.  It shows that racial harmony is not just a dream, but a real possibility.