Here's the plot of Thirteen:
Thirteen-year-old Tracy Louise Freeland (Evan Rachel Wood) writes poetry and is a straight-A student. Her divorced mother Melanie (Holly Hunter) is a recovering drug addict and high school dropout who struggles as a hairdresser to support Tracy and her older brother Mason (Brady Corbet). At Portola Middle School in Los Angeles, she is teased about her "cabbage patch" clothes by more popular girls. Melanie buys Tracy new clothing items from a discount vendor in a van. Thus clothed and much to her delight, Tracy is invited by Evie Zamora (Nikki Reed), one of the most popular girls at school, to go shopping on Melrose Avenue in Hollywood. Although Evie gives her a disconnected telephone number, likely as a mean-spirited joke, Tracy takes a bus to Melrose Avenue anyway, where she finds Evie and a friend shoplifting. Tracy later steals a woman's pocketbook while she is distracted and the girls go on a shopping spree, whereafter Tracy and Evie become fast friends and Evie moves into the Freeland house.
Meanwhile Tracy is angered by and torn between her divorced parents, both of whom are struggling to earn enough money to live. Unknown to her mother, Tracy has been cutting herself as a way to cope with her stress. Tracy neglects her old friends and at home taunts Melanie's boyfriend, a former cocaine addict (Jeremy Sisto). Melanie sees hints of what is happening with the two girls but is unable to stop them, further thwarted by Evie's manipulative but likely truthful claims of childhood abuse. As Tracy steadily shuts Melanie out of her life, Tracy and Evie become very close, even talking to each other in their own ludling language. However, after the early thrills, Tracy's newfound popularity doesn't make her happy.
In one scene, underage Evie and Tracy try to seduce Luke (Kip Pardue), a lifeguard in his early twenties who is a friend of Mason's. Drawn at first into their kisses, Luke throws them out of his house and soon after moves away. One night in Hollywood, Mason and a friend make comments about a cute girl who has her back to them. When she turns around and answers with a scathing remark, Mason is shocked to see this is his sister, with a belly ring. In another scene, the two girls take turns inhaling from a can of gas duster and become so high they laughingly hit each other for kicks, drawing blood.
Melanie isn't aware of how deeply the girls have fallen into petty crime and drug abuse, but seeing the harmful impact Evie is having on their lives, takes Evie back to live with Brooke (Deborah Kara Unger), her guardian, an aging model and aspiring actress who also works as a bartender and is going through a painful recovery from cosmetic surgery. Tracy seems to agree with this step, after which Evie betrays her at school.
Failing seventh grade, Tracy comes home one day to find Evie, Brooke, and Melanie waiting for her. When the women confront Tracy about the girls' drug use and stealing, Tracy angrily blames Evie. Brooke says Tracy was the bad influence and that they are moving to Ojai to get away from her. Melanie stands up for her daughter, saying Tracy was "playing with Barbies" before she met Evie. Brooke grabs Tracy and pulls her sleeve up to show Melanie the many cuts and long scars on her daughter's left arm. Melanie, taken aback and shaken by this sight, tells Brooke and Evie to leave. Both mother and daughter weep on the kitchen floor as Melanie kisses her daughter's heavily cut arm. Although Tracy tearfully pleads with her mother to let go of her, Melanie holds on tight and they wind up in Tracy's room where they carry on hugging and fall asleep. The movie ends the next morning as Tracy wakes up with a start. Tracy later spins alone on a merry-go-round in the park, screaming.
Jordan Wells (Jonathan Tucker), a photographer with an interest in photographing girls, meets Shay Bettencourt (Nikki Reed) at school. She wants Jordan to photograph her with an older man, Wade Chandling (Frank Whaley), for protection. In exchange, Shay will let Jordan photograph her. Shay tells Jordan that she is using Wade to help her get into Hartley, one of the top musical schools in the country. Soon after, Jordan and Shay become intimate. After finding out there has been no word from Hartley, Shay wants to get revenge on Wade by using the photos that Jordan took. When Shay meets Wade in the woods, Wade becomes angry and starts attacking Shay. Jordan tries to save Shay, but Shay ends up beating Wade to death. The two find ways to avoid implicating themselves when interviewed by detectives. Eventually, Detective Griffin (Michael O'Keefe) figures out that Shay only used Wade for the money he had, and he tries to set up an exchange with evidence on Jordan for the money. He tries to arrest Jordan during the exchange, but Shay shoots Detective Griffin. When Jordan is questioned by the police, Desiree (Julie Gonzalo) saves him by giving him an alibi. The film ends with Jordan driving away, narrating, "with a million dollars to decide what to do next."