Katherine "Katy" McLaughlin (Alison Lohman) has big dreams of administering her father's Wyoming horse ranch one day, but her father, Rob (Tim McGraw), has other plans. He is currently grooming her older brother, Howard (Ryan Kwanten), to take over the ranch and sends Katy away to an exclusive private school where she constantly feels like a misfit. Being a similar, independent spirit to Katy, Rob has a hard time understanding his daughter as she continually defies his authority to follow her own path.
When Katy comes home for the summer she is happily greeted by her family. In the early morning she takes one of their quarter horses out for a run into the great Wyoming wilderness. While resting on a log Katy decids that she is going to hace to tell her father about how she failed to complete her essay. While on the way back Katy gets bucked off of Yankee (the horse she was rideing) and gets chased by a mountain lion brifly. She ends ou falling down a shallow hill and she sees Flicka. Flicka and Katy both feel an instant connection with each other. Flicka then chases the lion off and then runs away back into the wilderness. When Katy gets back to the ranch she tells them all the story but is then confronted with Rob's disaprovel over not finishing her essay.
Later that day Katy trys to convince her father that they should bring the mustang in but Rob is not intrasted. Katy rides on of their quarter horses out to find Flicka. When she finds Flicka she runs after the mare and trys to lasso her but Katy falls of her horse and Flicka escaps. Flicka happens to run by the other horses and begains leading the heard away. while Howard, Jack and Gus round up the heard Rob catches Flicka with his lasso. While the horses are being led back Rob has Jack take Flicka so that he can talk to Katy. Katy says that she did not want the lion to get her horse but Rob says that Flicka does not belong to her or anybody else, he says she must have separated from some other mustang heard and he is surprised that the mare is still alive. Katy asks what her father is going to do with Flicka but Rob says that Flicka is not worth the price of a ball of hay. Gus then asks if Norbert was looking for a mustang, Rob the takes control of Flicka from Jack. While the quarter horse heard is lead into ther pen Flicka is put into a seprat pen. Katy rides back and tells them that the mustang is the wild horse and her mom Nell says that she is something and that she is about 2 years old and rob says about 2 years wild and that she is dangerous but Katy says that the mustang is just scared. Rob says that they should leave the horse alon but Katy says that Flicka will come down once she starts training her but Rob says that nobody is going near the mustang and that he is calling Norbert to take Flicka away cause he does not want a mustang around his horses. Katy says no to that and that she cane ride her but Rob says she can't and won't after the stunt she just pulled and that nobody goes near the wild horse without his permission. While she is running around in the pen Katy tells Flicka to calm down and they find out that Katy named the horse.
While they are sitting down to dinner Rob asks Nell how much the vet bill costs while everyone trys to avoid telling him, Nell ends up having to tell him and he becomes frustrated and rants about how when his father owned the ranch the horses were fine and took care of them selfs, Katy then shouts to him to not call Norbert to take Flicka away.
Nell then goes into Katy's room to talk. Katy says that she does not care what her father says cause Flicka is her horse, Nell asks Katy to let her talk to him but Katy says he does not listen when he is this mad, Nell then tells her dautgher that anger is just fear on the way out but Katy says he is not scared of anything and Nell tells her how when she was a 3 she wonderd outside the house and that she was found by Rob in lighting's stall, she says that horse could have killed her and she was laghing when Rob found her, she then tells Katy that you got to understand what it feels like to be responsible for something you love so much. Nell tells Rob to give her the horse and after Rob says no she says that Katy having her own horse would make her responsibal and she would feel proud of herself, Rob calls it pcyco babble and says it's about dicipline not pchycologe and that he won't reward bad behavior wich Nell says sounds like pyhcologe to her, Rob refuses to let Katy have Flicka.
That night Katy goes out to start training Flicka. While Flicka is still scared Katy sings to her "All the Pretty Little Ponies" to calm her down as she gets into the pen Flicka chases Katy out and Katy apologizes to Flicka. She sleeps on the ground until Jack wakes her up and tells her to wash up. That day Nell sees Katy getting started on writing her essay and decids to let Katy sleep.
The next night Katy sneaks into Flicka's pen and offers a calmer Flicka an apple to know if the mustang trusts her and Flicka comes over to get it showing that the horse trusts Katy. She then says that it's enough for tonight and leaves to get some sleep. Afterwords in the morning Howard and Katy drive off to a succluded acer of the ranch to do some work one the fence their. Howard tells Katy that they could get her a cheirot but she says that it would't be the same. She then says that as long he is their it would be his, he says that it wont be a problem because he won't be there. She says that she means on the ranch but he tells her that he knows what she means. He then tells her that he tried the ranch but it just was not working and he was going to talk the scholarship to B.U. He then asks her if she would tell him, she asks why would he want to leave Wyoming and he said burger joints whar you don't have to drive up throu the window but she says that he needs him to run the ranch. He then jokingly tells her that Rob dous not need him and that she is the one that he needs and that their father just dous not relize it yet.
The next night Katy pets Flicka and calls her a good girl. Katy the trys to put horse headgear on her but out of fear Flicka rises up and kicks Katy in the back of her sholder leaving a wound wich later heals. The next night Katy trys again but Flicka acts up. Katy is able to calm Flicka down and manages to get the headgear on and tells the horse that it was not so bad. She then heads back to bead happy and feeling proud.
On the next night when Katy was training Flicka and trys to ride her but she gets tossed off and Jack come in takes her out and tells her that she is not supposed to go in their. Katy asks what's it to him and he says its dangorus and that it is what her dad told her to. She asks him how long he is going to be afraid of her father and he says forever, he in turn asks her why she is going in at night if she is not scard and she says it's because she has to. He then tells her the she shoud not let anyone stope her.
Two nights afterwords Katy goes into Flicka's pen and the mustang comes right to her meaning that the horse knows her know. Katy gets on Flicka's back and succucfuly rides her. Katy then open the pen door so they can go out but Flicka starts to run and out of fear accadently bucks Katy of alerting her family. Gus and Jack ask her if she is alright and then go after Flicka. Rob, Nell and Howard go to mack sure that Katy is alright, Rob then tells Katy that she could not have pland a better way to get herself killed. Nell trys to calm him down but Rob says that she is not protecting Katy but crippling Katy and that she will be as usless as the mustang. Katy tells her father that Flicka is not usless and wants to learn but Rob says that she dous not. He tells Katy that she wants something that dous not exist and that it is time that she see the horse for what she is but Katy tells him that she knows who Flicka is, Rob than asks how she knows a damn thing about her and Katy says "Becaus we are the same". Rob is mad that she did this behind her back, Nell trys to tell him that Katy was excited and got carried away but Rob tells his wife not to mack excuses. Katy says that he just dous not get it and walks away and Howard follows. Nell trys to tell Rob that their has got to be a better way but Rob says that their is not. The next day Rob sells Flicka to Norbert who owns the rodeo, leaving Katy devastated. Nell tells Rob to unload Flicka before he looks like a damn fool, he than asks what is wrong with her and she says that he made the decision without her was because he know it's wrong but he says he is done dicussing it. Seeing his sister heartbroken over losing her beloved horse, Howard finally stands up to his father and says that Katy found Flicka so she should decide what happens to the horse. Rob says he will make the decissions around hear untill he is running the ranch then Howard finaly tells his dad that he does not want the ranch and that he wants to take the scolershipe. His mother Nell asks why he did not tell them that before and he says that its because running the ranch is what they wanted him to do, he then tells them that Katy wants the ranch and that he does not. The family becomes even more divided when Rob refuses to take Flicka back. Howard and Nell refuse to help Rob with the ranch.
While their parents are out one day Howard convinces his sister to go swimming with her and while thay are their Miranda comes and jumps in with them and they swim play with each other. Miranda tells Katy that she saw Flicka at the rodeo while practicing barral raceing and she tells Katy that she has never in her entire life been scard of horses but the horses she was with were dangerous and that you would realy need to work hard to mack horses that angry. Katy then concokts a plane to have Howard enter the race with her as his partner so that she can win the race and buy Flicka back with the prize money despite Howard's protests that this plan is to risky and dangorus. Miranda says that she is in and they get Howard to (reluctinty) be in on the plane and they jokingly push him back into the lake they were swimmming in.
At the wild horse race Howard and Katy (disguised as a cowboy) enter the competition that Flicka is being used in, hoping to get the horse back. Rob, however, catches onto his daughter's plan and tries to intervene. Katy freezes at the sight of her father, but Howard boosts his sister onto the mare's back and lets the two escape. Katy rides Flicka bareback and Flicka wins the race but instad of stoping at the finish line Katy rides Flicka out of the rodeo and into the mountains.
Lost in the mountains, Katy doesn't know how to get back home in the dark. Since she knows the terrain even in the dark, Flicka slowly makes her way back to the ranch, carrying Katy on her back. As a fierce thunderstorm moves in, the family reconciles and starts searching for Katy. As they near the ranch, Katy and Flicka are attacked by a mountain lion. Flicka protects Katy, but is severally wounded in the process. Katy throws a rock wich scares away the lion. Katy tries to get Flicka to get up but she is too injured to move. Katy ties her shirt around the mare's wounds and refuses to leave her. Already wet and cold, the girl quickly develops a high fever.
After searching for hours, Rob finds the two and brings a delirious Katy back to the house. As her fever spikes dangerously high, Katy calls for Flicka as Nell tends to her, hoping the fever will break. Rob thinks Flicka is mortally wounded and believes she should be put down. When his fellow ranchers Jack and Gus refuse, knowing Katy will hear the shot, Rob decides to do it. Overhearing the argument, Katy stumbles into the room and gives her dad permission to shoot the horse, saying "you can shoot us" as she cries.
Heartbroken by her words, Rob goes outside and begins to cry as he finally understands his daughter's feelings and her pain. Later, a gunshot is heard and Katy bursts into tears, thinking Flicka is dead. The next morning, Nell finds Rob walking back to the house, supporting the injured Flicka. She runs outside to help and finds out that the gunshot was him shooting at the mountain lion. Rob is stunned that the mare is still alive and Nell says that the reason Flicka is alive is because she has mustang blood and that she is a fighter just like their daughter and they decide not to put her down. Katy's fever breaks and over the next couple of days, she begins to recover. When Katy wakes from the fever, she and Rob reconcile and he takes her to see Flicka, whom Katy is shocked to see is alive Rob tells Katy that Nell has been talking good care of Flicka but when she gets better he expacts her to take care of Flicka herself. Rob also apologizes to Howard and gives his son his blessing. Thrilled, Howard begins preparing for college. As a family, they decide to not sell the ranch, making it both a working ranch and a refuge for wild mustangs. The film ends with Katy riding Flicka across the beautiful Wyoming landscape.