The short story "That Evening Sun" explores Southern race relations of the early 1900s. The Compson family's maid Nancy is terrified that her husband will kill her because she is pregnant with a white man's baby. Even though she was a servant to the Compsons, in order to make ends meet, she prostituted herself to a white man. The major tension, however, in the story, is the Compsons' reactions to Nancy's fear.
The context of the story is important to its developing conflicts, but the themes are universal. Mr. Compson tends to downplay Nancy's fear. Even though he recognizes that she may be truly in danger, he convinces himself that she will be all right because he knows Mrs. Compson, his wife, is opposed to his catering to the black maid. The children don't understand her fear, and will stay with her only because she is desperately attempting to bribe them. So we have here, a gutless husband, innocent children, and Nancy who is the victim of a society that provides her nowhere to turn. She cannot turn to the corrupt police who see her as little more than an animal, her husband who has become her potential attacker, and the white man who impregnated her --he beats her, refuses to pay, and has her arrested. These issues of injustice, corruption, passivity in the face of man's inhumanity to man, childhood innocence and coming of age, abuse of power--are issues that all people of all ages face.
I encourage you to read the enotes explanation of the story's theme. I posted the link below.