Chapter's 1 & 2
George and Lennie camp in the brush by a pool, the night before starting new jobs as ranch hands. George finds Lennie stroking a dead mouse in his pocket. He complains that caring for Lennie prevents him from living a freer life. We find out that Lennie's innocent petting of a girl's dress led to them losing their last jobs in Weed. However, when they talk about their dream of getting a piece of land together, we know they really depend on each other.
When they arrive at the ranch in the morning, George and Lennie are shown around by old Candy. They meet their boss and, later, his son, Curley - George is suspicious of Curley's manner and warns Lennie to stay away from him. They see Curley's pretty and apparently flirtatious wife and meet some of their fellow workers, Slim and Carlson.
Chapter's 3 & 4
Later that evening, George tells Slim about why he and Lennie travel together and more about what happened in Weed. The men talk about Candy's ancient dog, which is tired and ill. Carlson shoots it, as an act of kindness. George tells Candy about their dream of getting a piece of land and Candy eagerly offers to join them - he has capital, so they could make it happen almost immediately. Curley provokes Lennie into a fight, which ends up with Lennie severely injuring Curley's hand.
The following night, most men on the ranch go into town. Crooks is alone in his room when Lennie joins him. They talk about land - Crooks is sceptical, not believing that George and Lennie are going to do what so many other men he's known have failed to do, and get land of their own. Yet when Candy happens to come in as well, Crooks is convinced and asks to be in on it too. Curley's wife arrives. She threatens Crooks and an argument develops. Crooks realises he can never really be part of George, Lennie and Candy's plan.
Chapter's 5 & 6
Next afternoon, Lennie accidentally kills the puppy that Slim had given him by petting it too much. He's sad. Curley's wife finds him and starts talking very openly about her feelings. She invites Lennie to stroke her soft hair, but he does it so strongly she panics and he ends up killing her too. He runs away to hide, as George had told him. Candy finds the body and tells George. They tell the other men - Curley wants revenge.
Lennie hides in the brush by the pool. He dreams of his Aunt Clara and the rabbits he will tend when he and George get their land. George finds Lennie and talks reassuringly to him about the little place they will have together - then shoots him with Carlson's gun. When the other men find George, they assume he shot Lennie in self-defence. Only Slim understands what George did and why.