A group of the ranch hands have been left behind, deserted by the others who are out enjoying themselves a bit.
In this chapter, we see Lennie, who is socially at a disadvantage because of his mental challenges, reach out to Crooks, who is socially at a disadvantage because of his race in this era. Lennie feels a bit lost without George, and this loneliness prompts him to reach toward another person in friendship:
Lennie smiled helplessly in an attempt to make friends.
Crooks said sharply, “You got no right to come in my room. This here’s my room. Nobody got any right in here but me.”
Lennie meets rejection; Crooks is legitimately concerned about any possibility of incrimination against his character because black people in this era were regularly lynched. In fact, we see Curley's wife threaten just this later in the chapter:
Crooks stared hopelessly at her, and then he sat down on his bunk and drew into himself.
She closed on him. “You know what I could do?”
Crooks seemed to grow smaller, and he pressed himself against the wall.
“Well, you keep your place then, Nigger. I could get you strung upon a tree so easy it ain’t even funny.”
In these characters, we see loneliness fueling anger which leads to further isolation. Because Crooks is excluded from society, his anger about that isolation spills over onto Lennie's genuine attempts to befriend him. Lennie is thus left lonely without George's presence. Curley's wife is not well-suited for ranch life, and she has a wandering eye that longs for more than her husband can provide for her—especially in this setting. She feels isolated, without any real female companionship, and surrounded by men whom she can't relate to. When she enters the bunk house, she insults the men, commenting that the other men left all the "weak ones" behind, and then when she is asked to leave, she speaks to her own isolation:
Think I don’t like to talk to somebody ever’ once in a while? Think I like to stick in that house alla time?
After she strikes out at Crooks, Candy tries to defend him; Curley's wife insults him as well, telling him that if he dares speak against her, no one would believe him. He sadly agrees.
This group represents those who are isolated from their society, and their varied attempts to connect with others leave them bitter, frustrated, and detached. This sense of a group of individuals who are isolated even from each other furthers the bleak tone of the plot.