Lennie wonders into Crooks room in the barn because he thought he was lonely. Crooks asks Lennie a bunch a hypothetical questions about George because he went into town. Later, Candy comes in and tells Lennie about the numbers he's been crunching for their ranch. Crooks thinks their idea is crazy. Curley's wife runs into them again looking for trouble.
Lennie is playing with his puppy in the barn and when the dog tries to bite him he slaps the dog and kills it. Then he thinks about whether he should kill the dog or not and in the meantime Curley's wife comes in the barn looking for company. She discovers the dead dog and invites Lennie to feel her soft her. Lennie started stroaking her hair to aggressively so she jerked away and tried to yell.
Lennie feared all the men hearing Curley's wife's yelling so he closed her mouth but accidently broke her neck, killing her. Lennie snuck away while the men were playing horseshoe and took his dead puppy with him. Shortly after Candy came into the barn looking for Lennie and found the dead body. First he told George, and then George devised a plan for Candy to reveal the tragedy to the rest of the men and lead them in the opposite direction of Lennie.
A beautiful scenery is described, and then a ghost like figure of Aunt Clara and a large rabbit appear to Lennie and tell him all that he has done wrong to George. Lennie keeps trying to apologize, but the apparitions aren't satisfied. They leave and then George comes.
After the ghost rabbit tells Lennie George is going to leave him, he arrives and asks Lennie why he was yelling. George and Lennie talk about happy things, like how they have each other and their future farm.
George tells Lennie that everything is okay then he is able to get Carlson's gun off of Lennie and while they are talking about happy things, and Lennie is looking off into the sunset George shoots him with a shaky hand, but nonetheless kills him.