<P> Colin begins to like Lindsey, though he is foiled by her boyfriend, Colin (he and Hassan call him TOC, "the other Colin"). Colin is still chasing his eureka moment, finally finding it in his theorem he created called the Theorem of Underlying Katherine Predictability . The theorem determines the curve of any relationship based on several factors of the personalities of the two people in a relationship . His theorem eventually works for all but one of his past relationships with a Katherine--which the novel explores . </P> <P> While the back stories of Colin's life play out, Hassan gets a girlfriend, Katrina, a friend of Lindsey's . The relationship is cut short when Colin and Hassan catch Katrina having sex with TOC while on a feral hog hunt with Lindsey, her friends and Colin's father . A fight between TOC and all of the surrounding acquaintances begins when Lindsey finds out that he's been cheating on her . While injured in the fight, Colin anagrams the Archduke's name while in the grave yard to dull the pain, and realizes that it is actually Lindsey's great - grandfather, named Fred N. Dinzanfar, that is buried in the tomb . </P> <P> Colin finds Lindsey at her secret hideout in a cave, where he tells her the story of every Katherine he has ever loved . Lindsey tells him how she does not feel sad but instead slightly relieved by TOC's affair . They discuss what it means to them to "matter" and eventually confess their love for each other . As their relationship continues, Colin decides to use his dating formula to determine whether or not he and Lindsey will last . The graph reveals that they will only last for four more days . Lindsey then slips a note under his door, four days later, stating that she cannot be his girlfriend because she is in love with Hassan . But she leaves a P.S. stating that she is joking . Colin realizes that his theorem cannot predict the future of a relationship; it can only shed light on why a relationship failed . Despite this, Colin is content with not "mattering". Hassan also states that he is applying for two college classes, which Colin has been trying to convince him to do throughout the book . The story ends with the trio driving past the restaurant they were originally planning on going to, because Colin, Lindsey, and Hassan realize that they can just keep driving; there is nothing stopping them from continuing on . </P> <Dl> <Dt> Colin Singleton </Dt> <Dd> Colin Singleton is an anagram - loving seventeen - year - old boy who is depressed . Though he was a child - prodigy with an IQ of over 200, he has not yet become a "genius". Colin finds everything interesting, especially things that other people seem to not care much about . Because of this, it is difficult for people to relate to Colin . After only dating Katherines, Colin breaks the streak by dating Lindsey Lee Wells, who he met on his road trip with Hassan . Throughout the novel Colin feels as though there is a hole in his stomach, and he is looking to fill it . Colin spends his time striving to be unique, but with Lindsey's help, ends up coming to the realization that he is "not - unique in the very best way possible ." </Dd> <Dt> Hassan Harbish </Dt> <Dd> Hassan Harbish is Colin's lazy, funny, and slightly overweight best, and only, friend . Though he is smart and has been accepted to college, Hassan takes a year off . At first Hassan does not seem to plan furthering his education . He convinces Colin to go on a road trip in order to break out of his depression . Hassan is Muslim and takes his faith very seriously, acting with strict religiosity, until he dates Katrina . Hassan is an integral part to Colin's journey of finding his true identity . </Dd> <Dt> Lindsey Lee Wells </Dt> <Dd> Lindsey Lee Wells meets Colin and Hassan on their road trip in Gutshot, Tennessee . She is a paramedic - in - training who also gives tours of Gutshot . When Lindsey first appears in the novel, she is dating someone else named Colin, not the protagonist . However, she doesn't feel like she is truly herself until she starts hanging around Colin Singleton . Like Colin, Lindsey seems to be struggling with her identity . Inspired by Colin's ability to always be himself, Lindsey finally becomes herself . </Dd> <Dt> Hollis Wells </Dt> <Dd> Lindsey's mother . An extreme workaholic . Very kind to the people who work at her factory . </Dd> </Dl>

How many katherines are there in the world