The day after his graduation from high school finds Colin Singleton sitting in the bathtub, thinking about how he is getting too old to be a child prodigy, and how he wishes his ex-girlfriend, who dumped him the night before, would call him. Katherine, or more specifically, Katherine XIX, was the nineteenth girl Colin has dated. They have all been named Katherine, and all of them have broken up with him. Colin, who has always been called “special,” feels like he does not matter to anyone. Once he finishes his bath, he asks his parents to leave him alone so that he can lie abjectly on the floor, worrying that he will never have a “Eureka” moment in which he makes a new discovery, proving that he is an adult genius and not simply a washed-up child prodigy.
Colin’s best friend, Hassan Harbish, finds Colin stewing in his room and convinces him that they should go on a summer road trip so that Colin can get over Katherine. Colin agrees. Colin’s parents are easy to convince to allow him to go, in part because their parenting philosophy includes giving Colin the freedom to make his own decisions. (This allowance of freedom is how Colin got their permission last year to go on a television game show called KranialKidz, on which he won the ten thousand dollars that are now going to finance the road trip.) Still, they express disappointment that Colin is giving up his summer, which he could have used to take some college classes ahead of time now that he won’t have Katherine as a distraction. Colin’s father even suggests that Colin is “giving up” on his entire future. It is the first time Colin has disappointed his parents. Hassan, on the other hand, has been worrying his parents because he is a year out of high school, and although he has been accepted to college, he shows no interest in doing anything other than watching Judge Judy. Colin, with his better parental track record, convinces Hassan’s parents that he will be a good influence on Hassan and help him get a job. Their parents having reluctantly approved the plan, Colin and Hassan take off driving toward nowhere in particular in Colin’s Oldsmobile, which they call “Satan’s Hearse.”
While they drive, Colin thinks about the feeling he has in his gut regarding Katherine. It is as though she has taken a piece out of him, leaving behind a hole. His brain drifts to other historical and literary figures he knows of who have had holes in their guts. Namely, he thinks of the Archduke Franz Ferdinand. When he sees a sign on the road for the grave of the Archduke, he feels compelled to stop and visit it. Hassan, only wanting to stop somewhere, agrees.
The pilgrimage to the Archduke’s grave brings Colin and Hassan to the small town of Gutshot, Tennessee. There, they meet a girl their age named Lindsey Lee Wells who has dated only one boy, and coincidentally, he happens to be named Colin. Hassan and Colin decide that he will be The Other Colin, or TOC. Colin and Hassan end up staying in Gutshot with Lindsey and her mother, Hollis, who owns the local textile factory that produces mainly tampons. Hollis employs them as interviewers for a project on the history of Gutshot. When they are not working as interviewers, Hassan gets to know Lindsey’s friends while Colin works obsessively on a Theorem, which he believes will be his stroke of genius, to predict the course of any romantic relationship. However, over the course of their stay in Gutshot, Colin develops feelings for Lindsey that eclipse his obsession with the Katherines.
As a favor to Hassan, who has been feeling as though he lives in Colin’s shadow and as though Colin is resentful of him for making friends with the local Gutshot kids, Colin agrees one day to go on a wild hog hunt. Lindsey takes him out ahead of time to practice shooting, and they bond over their mutual feeling that they don’t matter. The day of the hunt, Colin and Hassan take a break in the forest. Colin calls Katherine III, who is giving him trouble with the Theorem. He finds out that contrary to his belief that every Katherine has decided he is not important enough to date, he is the one who broke up with Katherine III. Right after this revelation, a wild hog appears and begins charging Colin and Hassan. Colin accidentally shoots a hornets’ nest instead of the hog. They run out of the forest, pursued by hornets, and make their way to the graveyard, which is the only landmark they recognize. There, they find TOC and Katrina, the girl Hassan has just started dating, having sex on one of the graves. The two swear Colin and Hassan to secrecy. A while later, once Lindsey and TOC’s other friends show up, TOC is rude, and Colin (who has realized that he has feelings for Lindsey) decides to reveal that TOC has been cheating on Lindsey with Katrina. Everyone gets in a big fight, TOC kicks Colin in the groin, and Colin realizes in his dazed state that Franz Ferdinand is an anagram for the name of Lindsey’s great grandfather, Fred N. Dinzanfar.
A few days later, Lindsey brings Colin and Hassan on an espionage mission to find out the truth behind a rumor that Hollis is selling some of her land. They drive to the factory warehouse in Memphis, where they discover some of the factory workers burying huge boxes of tampons. Hollis shows up and explains that the factory is doing poorly because of overseas competition. Not wanting to fire anyone (to do so would be a massive blow to the Gutshot economy, not to mention the individual workers to whom Hollis feels an allegiance), she has been burying the unsold tampons so that her employees will not notice them stacking up. In the meantime, she has been trying to find alternative ways to bring in revenue, including selling land, and, as Colin and Lindsey discuss later, advertising the grave of her grandfather as the grave of the Archduke Franz Ferdinand to bring in tourist revenue.
That night, Lindsey and Colin escape to Lindsey’s secret hideout and discuss how selfless Hollis has been and how they both feel too selfish. They decide that in order to matter, they need to care more about things that really matter instead of the old grudges and obsessions that have dictated so much of their behavior up to this point. They have their first kiss in the dark in Lindsey’s secret hideout, and from then on out they begin dating in earnest. Hassan is happy for Colin, but has decided that for himself, he is no longer going to date anyone until he is ready to get married. He has also decided to register for some college classes and start taking a more active role in his own life. The world seems balanced again, except that Colin is now dating a Lindsey instead of a Katherine.
The only problem is that the Theorem Colin has worked so hard to perfect seems to indicate that Lindsey will break up with Colin in four days. On the morning of the predicted breakup, Lindsey leaves Colin a note saying that she has run off with Hassan. “P.S.,” she writes, “Just kidding.” Colin then has his greatest “Eureka” moment when he realizes that the Theorem might work to model past relationships, but that there is no way to predict the future. He decides to relinquish some of his control and just let life happen: once he lives it, he can rearrange the events to tell any story he wants, just like he rearranged the events with Katherine III to fit the story of his perpetual “Dumping.” The novel ends with Colin, Hassan, and Lindsey driving down the highway, going nowhere in particular and excited to see where they will find themselves.
