For introverted Cather, her freshman year of college at the University of Nebraska in Lincoln is terrifying. For her identical twin, Wren, it is an adventure. Cather hates that Wren did not want to share a room with her and has forced her to live with a complete stranger, a girl named Reagan with an ever-present boyfriend named Levi.
Cather’s anxiety is such that she will only leave her room to go to class. Instead of eating in the dining hall, she makes do with power bars and peanut butter that she brought from home. Meanwhile, Wren is fully embracing college life. She and her roommate, Courtney, have become best friends and regularly party at the frat houses.
The only thing that eases Cather’s nerves is writing Simon Snow fanfiction. (Excerpts from the Simon Snow books and Cather’s fanfiction story, Carry On, begin every chapter.) While fans of the magical book series eagerly await the release of the eighth and final novel, they hungrily eat up Cather’s fanfiction story based in Snow’s world. She has thousands of devoted readers dying to know more about the homosexual love story she has created between Simon Snow and his arch nemesis, Baz. Cather finds it difficult to write however, with Levi’s constant presence in her room.
After a month, Reagan confronts Cather and accuses her of having an eating disorder. Cather finally admits that she does not know where the dining hall is and that she can’t handle the stress of eating in front of strangers. Reagan, an intimidating upperclassman, forces Cather to go to dinner with her. Although their initial conversations are antagonistic, the two eventually become friends.
Their favorite pastime is to make up stories about the other students in the dining hall. Cather also makes a friend in Nick, a fellow writer in her advanced-fiction writing class. He and Cather pair up to write a story for the class, and the story is well-received. They decide to meet at the library to work on another story together. Levi insists on walking Cather to and from the library at night, since Nick doesn’t offer.
Just when everything is going well for Cath, things begin to turn sour. Cather’s mother, who left when Cather and Wren were 8, starts talking to their father. She wants to try and have a relationship again with her daughters. Wren is open to the idea, but Cather is not. She will not forgive her mother for dumping them.
Cather receives another blow when her fiction professor gives her an F and accuses her of plagiarism for writing an assignment using the characters from the Simon Snow books. Desperate to cheer herself up, Cather returns to her dorm room and lip syncs to Kanye West songs on her laptop.
When Levi shows up, he joins in the fun until Cather receives an emergency text from her sister. Levi drives her to a bar just off campus, where Wren is drunk and dancing. She accidently sent the text to Cath. It had been a code for her roommate, Courtney, to come because a boy she liked was at the bar.
While Cather tries to get Wren to leave, Levi defends their honor from drunk patrons who want to see the hot twins make out together. Wren refuses to go back to her dorm room and sober up, so Cather and Levi are forced to let her walk away with Courtney and a boy named Jandro.
Thanksgiving at Cather’s house is not particularly festive. Wren has been talking to their mother and has agreed to spend Thanksgiving afternoon with her. Cather is furious. Especially when Wren does not return home for Thanksgiving dinner with her and their dad.
Cather returns to college and is glad when Levi comes by looking for Reagan for a study date. Unfortunately, Reagan is out. Levi admits to Cather that he has a learning disability and can’t read. Reagan has been summarizing books for him so he can keep up in class. When Reagan does not return to the room, Cather agrees to read to him. Eventually, Levi joins her on her bed. Many hours later, tired and emotionally spent from the story, Levi and Cather end up sharing several drowsy kisses then falling asleep.
Reagan is shocked when she comes home the following morning to find them in bed together. She gets over it quickly, as she admits that although she and Levi dated in high school, they are now only friends. Embarrassed at her behavior, Cather will not agree to go to a party at the house Levi shares with several other guys.
Reagan convinces her otherwise, but Cather is crushed when they see Levi kissing another girl in the kitchen. Reagan immediately takes Cather back to their room. Neither tells Levi what they saw, and Cather refuses to answer any of his texts. She also finds excuses not to be in her room when he is there with Reagan.
As the end of the semester approaches, Cather worries about her father. He is not answering her phone calls and has a bi-polar disorder. Another blow comes when her writing friend, Nick, tells her he is going to turn in the story they had been working on together for his final project in their writing class. He justifies this because he has worked on it outside of the time they spent on it together in the library. Although she is angry, she runs back to her dorm room without telling him. She spends hours trying to write her own story, but ends up falling asleep.
A phone call from her father’s co-worker wakes her up. Her father has been admitted to the hospital after one of his manic episodes. Cather calls Wren, who says they should wait until they take their finals to visit; after all, he will be medicated for several days.
Desperate for a ride to Omaha, Cather calls Levi. He immediately leaves work to pick her up. As they wait at the hospital, Cather finally tells Levi she saw him kissing another girl. Although Levi tries to explain that it meant nothing, he makes the situation worse. Cather asks him to leave when she is finally allowed in to see her dad.
Cather stays in Omaha to clean the house, do laundry and prepare for her father’s return. He and Wren arrive home just before Christmas. Although they try not to fight, she and Wren have a huge argument when Wren says she is going to spend Christmas Eve with their mother. Once the holiday is over, Cather admits to her father that she does not want to return to the University of Nebraska in Lincoln. He makes a deal with her. She will return for the spring semester and can quit after that, if she is still unhappy.
Cather speaks to her advanced-fiction professor, who has given her an incomplete for not turning in her last story. Cather wants to take a D, but the professor convinces her to take a chance and try writing the final story. Levi returns, apologizing for everything, and begging for a second chance with their relationship. Cather agrees to both of them.
Cather and Levi take their relationship slow for several weeks, as Cather does not want to get hurt again. Levi is at home one weekend when Cather receives a call from her mother. She is with Wren at a hospital in Lincoln. Wren was dropped off, unconscious, with alcohol poisoning. In the waiting room, Cather talks with her mother for the first time in 10 years, but she has no forgiveness to give her.
After a doctor comes out to tell them that Wren is still unconscious but expected to make a full recovery, their mother goes home without seeing her, leaving a furious Cather to wait alone. Later, when Wren is released, Cather is surprised to find Levi in the waiting room. He drove back to Lincoln to make sure Wren was going to be OK. Cather and Wren make up after her sister’s hospitalization.
Cather and Levi’s relationship intensifies, and it gives Cather new confidence in herself and the future. She is surprised to find Nick outside her dorm room one night. His story has been selected for publication in the school’s prestigious literary journal, but only if he gets Cather’s permission to print it and gives her co-author credit. With Levi, Wren and Reagan by her side, Cather refuses to grant him her permission.
Invigorated by her newfound courage, Cather throws herself into writing her fanfiction story. She is desperate to finish it before the final novel is released, but when Levi finds out she has devoted all her time to that, and none to writing a story for her advanced-fiction teacher, he gets angry. She is throwing away an opportunity that he would kill for, and possibly ruining her chance to keep her scholarship.
They have a major argument but make up soon afterward. His words make Cather realize there is more to life than Simon Snow. She sits down and writes a story based on her own life, beginning after her mother left. The story wins the underclassman fiction prize and is published in the university’s literary journal.