The novel opens as fifteen-year-old Julia Reyes and her parents, whom she calls Amá and Apá, are looking into the casket of Julia’s recently-deceased older sister, Olga. Olga, who was always the prim and proper “perfect Mexican daughter” and Amá and Apá’s favorite, was recently run over by a semi on the streets of Chicago while crossing the road to transfer buses. Amá was supposed to pick Olga up from her job at a medical office on the day of the accident, but when the hotheaded Julia got in trouble at school, Amá was forced to get Julia instead, and so Olga was left to take the bus home. Though Julia is saddened by her sister’s death, she’s put off by her mother’s crazed emotional display, and by the attention-seeking grieving she sees her nosy aunts engaging in. Julia’s best friend Lorena shows up to comfort her, and as Julia hugs her friend, she sees over Lorena’s shoulder a strange man who she assumes is a very distant uncle.
After Olga’s funeral, Amá takes to bed and doesn’t get up for several weeks. There’s no food in the house, there are roaches everywhere, and Julia’s father will barely look at her. Julia tells Amá that she needs to get up and get on with her life, and though she initially balks at Julia’s telling her what to do, she does indeed get out of bed, shower, and make some tea. She sits Julia down at the kitchen table and tells her that she’s planning on throwing Julia a quinceañera—a festive celebration which marks fifteen-year-old Latina girls’ transition into womanhood. Julia says she doesn’t want the party—the family doesn’t have the money, and she’s going to be sixteen soon, anyways. But Amá is firm. She never had the chance to give Olga a quince, and she is not going to make the same mistake twice. That night, unable to sleep, Julia gets out of bed and wanders into Olga’s room. She begins looking through her sister’s things and finds a few mysterious items: a note that reads “I love you,” a box of sexy lingerie, and a key card to a hotel downtown called The Continental. Julia finds Olga’s laptop under her bed and tries to enter the password, but can’t guess it. She stashes the laptop back under the bed and falls asleep in Olga’s room. In the morning, knowing Amá will be angry to find her in her sister’s room, Julia tries to sneak back to her own bed, but she is caught and grounded.
Julia hates being grounded, and yet finds herself in trouble all the time for even small infractions. She daydreams about getting away from her strict mother and living a freewheeling, independent life as a writer in New York, but every new punishment just demoralizes her further. On the day her punishment is lifted, Julia heads downtown after school to visit The Continental in hopes of getting some answers about Olga. The concierge, though, refuses to release any information about hotel guests, and Julia leaves feeling defeated. She visits the art museum on her way out of the city, and gazing upon her favorite painting—the brutal Judith Slaying Holofernes—reignites her determination to find answers about Olga. Julia searches for answers from Olga’s best friend Angie and even uses the internet at Lorena’s house to try and Google information about Olga, but everything is a dead end. However, when Julia meets one of Olga’s high school friends Jazmyn at a masquerade party she’s attending downtown with Lorena and her new flamboyant friend Juanga, Jazmyn mentions that Olga was “in love” the last time she saw her a few years ago. Julia becomes determined to follow this new lead. Julia becomes obsessed with tracking down old high school classmates of Olga’s. But as Julia’s mental state visibly deteriorates, her kindly English teacher Mr. Ingman begins to worry about her. Julia insists she’s fine—even as the holidays approach and her nonstop detective work causes her to stay out later and later and get grounded by Amá more and more often.
The holidays pass in a blur, and Julia’s erratic behavior and fiery diatribes continues to confuse her friends and family members. She alienates Lorena and Juanga when she attacks them for criticizing her aloofness one day during a field trip, and continues to refuse help from Mr. Ingman. Julia visits the community college where Olga took classes in hopes of securing her sister’s transcripts, but the registrar is unhelpful and refuses to share any of Olga’s information. Julia and Lorena reconcile, but Lorena, who’s worried about Julia, urges her to give her search for more information about Olga a rest—maybe, Lorena says, Olga really was “perfect.” Julia tries one last time to get some intel by asking Juanga to help her get Jazmyn’s number, but when Julia calls her sister’s friend up, Jazmyn can’t remember anything about Olga’s secret boyfriend other than the fact he had a “good job.”
Julia’s quinceañera arrives. The event is a disaster. Julia is uncomfortable in her frilly, ridiculous party dress, and wishes that she could spend the night reading a book alone in the corner rather than dancing. When her Tía Milagros mentions something about Olga while talking to Julia in the bathroom, Julia flies off the handle and begins excoriating Milagros for her nosy, passive-aggressive ways, and at the end of the night Amá and Apá confront Julia about her hateful ways. Amá suggests that if Julia could just have learned to keep her mouth shut, Olga might still be alive—referencing the incident at school which pulled Amá away from Olga and forced her to take the bus home on the fateful day of her death.
Julia spends the summer cleaning houses with her mother. In the fall, she allows Mr. Ingman to help her prepare for standardized tests and college admissions essays, determined to get out of Chicago. One afternoon, when school gets out early, Julia heads to downtown Chicago to visit a bookstore. There, she meets a cute boy named Connor who flirts with her about literature and takes her out for coffee. When Julia tells Connor about Olga, and her fruitless search to find out more about the secret life her sister might have had, she mentions Olga’s locked laptop, and Connor offers to help her hack into it. As the weeks go by and fall turns to winter, Julia spends more and more time with Lorena and Juanga, and meets up with Connor whenever she has the chance. She is genuinely happy, even though a year after Olga’s death, memories of her sister still haunt her. Connor invites Julia to his parents’ fancy house in the affluent suburb of Evanston and they have sex for the first time, even though Julia feels embarrassed and apprehensive about the cultural and class divides between them. After returning home from Connor’s, Julia goes into the freezer to heat up some waffles—the only food in the house—and finds the key to Olga’s room—which is kept locked—stashed inside. That night, she goes into Olga’s room and removes her laptop, the lingerie, and the hotel key card. She stashes the laptop in her backpack but puts the lingerie in a box in her closet. The next day, when she arrives home from school, she finds that Amá has gone through her things and found the underwear—she believes it is Julia’s, and Julia doesn’t try to convince her otherwise. She is placed under the most intense grounding of her life, and resorts to contacting Connor using a pay phone near school. Each day she complains to Connor about how bad things are at home and how hopeless she feels, and one day he admits that he doesn’t know how to help her. Feeling lost and alienated, Julia wanders around downtown Chicago in the snow, hungry but out of money, and considers how hopeless her life is.
Julia attempts suicide by slitting her wrists and wakes up in a hospital bed the next morning with her concerned parents standing over her. A psychiatrist, Dr. Cooke, meets with Julia privately and asks her to speak about all the things that have led her to the brink. Julia describes her unhappy home life, her contentious relationship with her mother, her feelings of hopelessness that she’ll ever be able to achieve her dreams and escape poverty, and her grief over Olga’s death. Dr. Cooke admits that Julia has a lot on her plate—but says that if she agrees to a weeklong outpatient intensive and weekly therapy thereafter, she can go home the next day. Julia agrees, and starts the outpatient program a few days later. Each day, Julia meets several teens her age who are struggling with serious problems, too. Each night, she goes home to have dinner with Amá and Apá. One night, they tell her that they’re sending her to Mexico the following week to get some time away and reconnect with family. When complaining about the trip to another girl in her outpatient program, Tasha, Tasha remarks how lucky Julia is to be able to get out of Chicago for a while, and Julia begins looking forward to the trip. The night before she leaves, Julia sneaks into Olga’s room one more time. She goes through papers in Olga’s desk, hoping to find Olga’s laptop password written down somewhere. After a few minutes of looking, she does. She enters the code and is able to get into Julia’s laptop and email—where she finds hundreds of emails sent back and forth over the course of several years with an anonymous married man; her lover. Julia keeps the piece of paper with Olga’s information written on it, hoping to be able to use it at an internet café in Mexico; the bumpy flight there, however, jostles her water bottle and ruins the paper.
In Mexico, Julia reunites with her family: Amá’s mother, Mamá Jacinta, a warm and gregarious woman; her aunts Fermina and Estela, who tenderly dote upon her; her good-humored Tío Chucho; and her cousins Belén, a beautiful girl about Julia’s age, and Andrés, a kind young man in his early twenties. Julia feasts on delicious food, spends warm summer nights outside with her aunts and cousins, and attends local football matches with Belén, who introduces her to a handsome young man named Esteban. There is trouble in her family’s small village of Los Ojos, though; the local narcos, or drug lords, have begun inciting violence in the neighborhood, and Chucho must bribe them regularly to prevent them from recruiting the innocent Andrés into their service. In Mexico Julia feels both comforted by her family’s presence and hyperaware of the violence lurking just beneath the surface. One day, on a trip into town, Fermina asks her how things are going at home. When Julia reveals that she and Amá have a difficult, contentious relationship, Fermina tells Julia a secret: when Amá and Apá left Mexico and crossed the border illegally into America, Amá was raped by the coyote leading them through the desert while Apá was forced, at gunpoint, to watch. The stunned Julia realizes that not only has her mother been hiding this secret from her all these years, but that Olga is not truly Apá’s daughter—the timing of her birth nearly a year after their arrival in the US means she was the product of Amá’s rape. As the violence in Los Ojos worsens, Mamá Jacinta tells Julia she must return to Chicago—before Julia leaves, Mamá Jacinta begs her to take good care of Amá. The day before she leaves, Julia discovers a cache of beautiful drawings done by Apá when he still lived in Los Ojos, and stashes a couple in her bag to bring back to her father.
Back in Chicago, things are slightly easier. Amá is happy to have Julia back, and apologizes for how tough things have been between them. Julia can barely look at her mother, pained by the secret knowledge she now has but doesn’t want her mother to know she’s learned. Julia gets her cell phone back, and is able to contact Connor, who reveals he has been worried sick about her for over a month. They make a plan to meet up downtown later in the week. Julia sneaks back into Olga’s room on her first night back in town and resumes reading the email chain she never got to finish—the final email, sent just a day before Olga’s death, reveals that Olga was pregnant with her lover’s child. Enraged and confused, Julia goes to hunt down Angie at the hotel where she works, and confronts her about Olga’s secret. Angie takes Julia out for coffee and reveals that though she knew the truth about Olga all along, she didn’t feel it was her place to tell anyone, especially after Olga’s death—the truth, she says, would only hurt everyone. Later, Julia meets up with Connor, and the two of them agree to see one another casually until they both leave for college.
One afternoon, Julia takes the bus to Olga’s old office, where she sits in the waiting room, unsure of what she’s hoping to find. She has deduced that Olga’s boyfriend must have been one of the doctors in the practice. When the mysterious man from the funeral walks in and is greeted by the receptionist as “Dr. Castillo,” Julia slips out and waits for him in the parking lot. She confronts him when he emerges at the end of the night, and he offers to take Julia to a diner and explain everything. At the diner, while Julia orders a huge dinner, Castillo explains that he did truly love Olga and wanted to leave his wife for her. Julia berates him for his inaction, but Castillo insists that one day Julia will understand just how complicated relationships can be. He gives Julia Olga’s ultrasound photo, and the disgusted Julia leaves.
Julia is doing well in therapy and feeling better than ever thanks to her new medication. She is accepted to NYU on a full scholarship, and excitedly tells her parents she wants to go. Though they’re sad she’s leaving, they support her decision. As the weeks go by, Julia spends time talking through her issues with Dr. Cooke and hanging out with Connor in secret on the weekends. Soon, it’s time for her to leave for New York. She bids tearful goodbyes to Lorena and her parents, and as she boards the plane that will take her to her future, she embraces the nervousness and uncertainty she feels about what’s to come. She reflects on how her journey to understand her sister better has actually taught her more about the “beautiful and ugly” pieces and parts of herself.