What is the mood in "Thank You, M'am"?

The mood of a story consists of the elements the author uses to make us feel a certain way while we are reading. This can include elements like description, setting, metaphors, and similes.
The setting of a story is especially important to establish the mood because it gives you a picture of where the story occurs, and how the characters react to those surroundings. In "Thank you, M'am," the setting is eleven o'clock at night on the street, with very few people around. To show us the setting, the author points out the time, and that the woman is walking alone at night. This gives the story an ominous mood.

It was about eleven o'clock at night, and she was walking alone...

The mood of the conversation between the boy and the woman can be seen by looking at the length of their sentences and the tone of their voices. The woman talks loudly and angrily, while the boy whispers and uses short phrases when he talks. Their interaction is brusque on her end and frightened on his end. The author describes the boy as thin, with shabby clothing. This shows a contrast between the boy and the woman, who is a "large woman." By describing the sweat "popping out" on the boy's face, and his tone of voice during their interactions, the author creates a mood of fear and intense anxiety.
Later, the mood in the story changes. When the woman drags the boy to her house, he realizes that there are other people in the house and that the door is open. This detail shows us that he still feels wary, but he feels safer now because there are other people around. The woman shows caring for the boy by telling him to wait till the water gets warm before washing his face. As the story progresses, the boy (who we now find out is named Roger) relaxes and can sit down and eat dinner with the woman. The mood of the story becomes much more comfortable, relaxed, and friendly. The story ends on a note of gratitude. Roger feels grateful to the woman for how she treated him, but doesn't know how to express it besides for saying, "Thank you, M'am" when she walks him out.