Meet Mattie Ross. She's a fourteen-year-old girl who likes One Direction, shopping at Hollister, and ponies.
J/K. Well, she does like ponies—but only if she's advising her dad to buy low and sell high. And when we meet Mattie, her dad Frank is doing just that, heading off to Fort Smith, Arkansas, to buy some ponies. He's traveling with his hired hand, Chaney, who makes a dumb move by gambling away his paycheck, getting drunk, and then deciding to go get his money back. By force. When Frank tries to stop this disaster, Chaney shoots and kills him.
Mattie hops on a train to Fort Smith, 70 miles from the Ross family home, to take care of her father's body and, more importantly, to get some dudes to help her track down Chaney. Specifically, she wants Reuben J. "Rooster" Cogburn, a mean US Marshall who shoots to kill. Perfect. He agrees; score! Unfortunately, a bossy Texas Ranger by the name of LaBoeuf (pronounced "LaBeef") has been tracking Chaney for years, and wants to keep tracking him with Rooster's help, but without Mattie's.
Just like Kate running after Jack and Sawyer, Mattie follows the two men into Indian Territory and nags them into letting her tag along. They learn that Lucky Ned Pepper's gang is planning to rob a train and that Chaney has teamed up with the gang. Score! They decide to spend the night in a hut, but it's already occupied—by two young men who are part of Pepper's gang. Double score! These two men kill each other while Mattie looks on, but not before giving up valuable information—Ned Pepper and the gang are planning on coming here to the dugout after they rob the passenger train.
Things are off to a good start, right? Too bad it all starts going downhill. Mattie, Rooster, and LaBoeuf wait in the woods to ambush the bandits, but LaBoeuf shoots prematurely. He kills Pepper's horse, but Ned Pepper and some of his gang dodge the bullets. Mattie and Co. plan to sneak up on them in their bandit stronghold in the Winding Stair Mountains. After a rocky climb, our avengers camp out in the mountains. The next morning, Mattie wakes up and walks down a hill to look for water—and comes face-to-face with her father's killer. When she threatens to shoot him if he doesn't come along, he laughs at her… so she shoots him in the side. (He stops laughing.)
Unfortunately, he isn't dead. Rooster and LaBoeuf show up to rescue her, but Lucky Ned Pepper and the other bandits make their appearance at the same time. They take Mattie hostage, promising to let her go safely if Rooster and LaBoeuf retreat. Rooster and LaBoeuf beat it, and Ned Pepper and his gang leave Mattie with Tom Chaney. He's supposed to deliver her to a safe place when it gets dark, with the threat that he won't get his share of the loot if anything happens to her.
Of course, Mattie's a sensible girl and doesn't trust this plan at all. She throws hot water at him, but he grabs her, hits her with his gun, and is just about to toss her into a snake-pit when LaBoeuf moseys on over to rescue her. Meanwhile Rooster is blocking Pepper's gang's exit from the mountains. A bloodbath ensues. Ned Pepper and most of his gang are killed, alone with Rooster's horse. Sad face.
While LaBoeuf is celebrating, Chaney bashes his skull in with a rock. Oops. Mattie shoots Chaney in the head, killing him but also falling backwards into the snake pit and breaking her left arm. Double oops. In the pit, she finds a man's skeleton … and a ball of snakes.
As Chaney taunts Mattie from the top of the crevice, Rooster shows up and … bashes his head in, of course. Chaney into the pit on top of the skeleton and wakes up the snakes. Smooth move, doofus. One of the snakes bites Mattie on the hand before Rooster and LaBoeuf can pull her out of the pit. Rooster rushes her off to a doctor, but it's too late: her left arm has to be amputated.
Fast-forward 50 years. Mattie never married, but she's an extremely successful businessperson. She never saw Rooster again; when she went to visit him, she found out that he'd died only a few days before. She also never heard from LaBoeuf again—but she hopes he'll read her story and hit her up.
You know what? We hope so too.