The Nineteenth Katherine
The story opens with Colin Singleton, a recently graduated child prodigy, reeling from his nineteenth breakup with a girl named Katherine. This Katherine, K-19, dumped him via email, leaving him devastated and feeling like a perpetual dumpee. Colin is obsessed with the pattern of his romantic failures, specifically with girls named Katherine. His best friend, Hassan Harbish, finds him wallowing in self-pity and urges him to do something drastic. Colin, known for his anagrams and intellectual pursuits, feels his prodigy status is fading and he's not living up to his potential. He believes there must be a mathematical explanation for his repeated heartbreaks, and he yearns for a grand, unifying theory to predict the trajectory of relationships.
The Road Trip Begins
To snap Colin out of his funk, Hassan suggests an impromptu road trip, just the two of them. They pack up Hassan's car and head out, leaving their hometown of Chicago behind. Hassan, a more laid-back and religious individual, is a foil to Colin's intense intellectualism. Their initial destination is unplanned, driven by a desire to escape Colin's misery and find a new perspective. Colin brings along his extensive intellectual baggage, including his obsession with Katherines and his desire to prove a mathematical theorem that will explain his romantic misfortunes, which he internally dubs 'The Theorem of Underlying Katherine Predictability'.
Arrival in Gutshot, Tennessee
Their road trip takes an unexpected turn when they arrive in Gutshot, Tennessee, a seemingly unremarkable town. They stop at a general store, where they encounter a young woman named Lindsey Lee Wells, who works there and also gives tours of the town's historical sites. Lindsey quickly becomes intrigued by Colin and Hassan. The town itself is peculiar, with a distinct lack of Katherines, which Colin finds both relieving and unsettling. The boys decide to stay in Gutshot for a while, drawn by the town's charm and the prospect of a new, distraction-free environment for Colin to work on his theorem.
The Archduke Franz Ferdinand's Grave
Lindsey takes Colin and Hassan on a tour of Gutshot, revealing its most unusual claim to fame: it's supposedly the burial place of Archduke Franz Ferdinand, whose assassination sparked World War I. This historical quirk is, of course, a fabrication, but it's a deeply ingrained part of Gutshot's local lore, perpetuated by a wealthy, eccentric local named Hollis. This discovery fascinates Colin, who sees parallels between the town's manufactured history and his own attempts to impose order and predictability on chaotic personal experiences. He also begins to develop a crush on Lindsey, further complicating his Katherine-centric worldview.
Hollis and the Factory
Hollis, Lindsey's mother and the owner of the local tampon string factory, takes an interest in Colin's intellectual prowess. She offers Colin and Hassan a job: to interview all the factory workers and document their life stories. This task gives Colin a new, real-world application for his analytical mind, diverting him from his singular focus on Katherines. It also allows him to spend more time with Lindsey, as she often accompanies them or helps facilitate their interviews. Hassan, meanwhile, enjoys the relaxed atmosphere and makes new friends in the town, finding a sense of belonging that Colin still struggles with.
Developing The Theorem
While working for Hollis, Colin continues to develop his 'Theorem of Underlying Katherine Predictability.' He creates complex mathematical equations and graphs, attempting to map the rise and fall of romantic relationships based on various factors, hoping to predict the exact moment he will be dumped. He uses his past relationships with the Katherines as data points, meticulously analyzing every interaction and emotional fluctuation. This intellectual pursuit becomes his coping mechanism, a way to regain control and understanding in a world he perceives as chaotic and unpredictable, particularly in matters of the heart. Lindsey, though initially skeptical, becomes a sounding board for his theories.
Lindsey's Secret Life
Colin's growing affection for Lindsey is complicated when he discovers she has a secret boyfriend, a boy named Katrina (a male, ironically) from a neighboring town, and that she often lies to both him and her mother. This revelation deeply upsets Colin, as it mirrors his own past experiences of being misled or hurt in relationships. He confronts Lindsey, feeling betrayed and once again confirming his belief in the unpredictable and painful nature of love. This incident fuels his determination to perfect his theorem, believing that if he can predict such outcomes, he can avoid future heartbreak.
The Pig Hunt and the Revelation
Hassan, Colin, and Lindsey go on a wild pig hunt, a local Gutshot tradition, with Hollis and Katrina. During the hunt, a feral hog attacks Colin, leading to a moment of intense fear and a subsequent conversation with Lindsey. In the aftermath, Lindsey confesses her reasons for lying and her own struggles with identity and expectations. This shared vulnerability and the raw experience of the hunt force Colin to look beyond his intellectual constructs. He begins to realize that life and love cannot be reduced to equations, and that focusing solely on predicting the future prevents him from living in the present.
The Theorem's Flaw
After the pig hunt and his conversations with Lindsey, Colin has a realization: his theorem, while mathematically sound in its own terms, fundamentally fails to account for the messy, irrational, and beautiful complexities of human emotion and free will. He understands that relationships are not predetermined and that trying to quantify love is a futile exercise. The theorem can describe past patterns, but it cannot predict future ones with certainty because people change and grow. He acknowledges that his obsession with the theorem was a way to avoid genuine connection and vulnerability.
Hassan's Commitment and Departure
Hassan, who has been enjoying his time in Gutshot and growing close to a local girl named Katrina (the same one Lindsey was seeing), decides he wants to stay in Gutshot for a while longer. He commits to studying seriously for the SATs, something he had previously put off. This decision marks a significant step in Hassan's own development, moving from aimlessness to purpose. Colin supports his friend's choice, recognizing that Gutshot has offered both of them a chance for growth and self-discovery. Hassan's newfound direction provides a contrast to Colin's ongoing internal journey.
A New Beginning
With his theorem reevaluated and Hassan settled, Colin prepares to leave Gutshot. He has a final, honest conversation with Lindsey, where they both acknowledge their feelings and the lessons learned. Colin realizes that his past relationships with Katherines don't define his future, and that genuine connection requires living in the moment and accepting uncertainty. He finally kisses Lindsey, signifying a departure from his Katherine-centric past. The ending suggests that while his mathematical genius remains, he now understands its limitations in matters of the heart, ready to embrace life's unpredictability.