After going on a road trip post-graduation, Elle (Joey King) still hasn't made her mind up about whether to go to Berkeley or Harvard - although Noah (Jacob Elordi) is already planning to get an apartment off-campus for the two of them. When Noah and Lee's (Joel Courtney) parents announce they're selling the beach house where they all spent their childhoods, Elle, Noah, Lee and Lee's girlfriend, Rachel (Meganne Young), offer to spend the summer there to help out with the sale.Lee starts to plan on how he can spend time with Rachel, who's going to a different college, while Elle is suddenly faced with a deadline by Berkeley. She chooses to go to Harvard with Noah which annoys Lee, but Elle promises to make it up to him by spending the summer doing their beach bucket list of various activities (Swim with the sharks, atomic wedgie to Noah, Cliff jumping, sky diving, Sandcastles, Pie eating contest, Brain freeze and so on, helium karaoke and so on).Noah's friend Chloe (Maisie Richardson-Sellers) - who Elle once thought Noah was having an affair with - arrives at the beach house to make things more complicated (Chloe's parents are getting divorced and Noah gets close to her, comforting her), and they all have a heated argument. Before that Chloe makes a light comment about Elle being very good at video games. Meanwhile Elle runs into Marco at the beach as well. When Elle tells Noah, he is angry, and Elle says that's a double standard as she OK having Chloe in the house.Noah and Marco (Taylor Zakhar Perez) clash at the go-kart track (Elle had asked Noah to dress up as Wario, but he refused and Marco had stepped up, while Elle dressed as Mario and Lee as the Princess. Noah went to race with Marco, but Marco ended up beating him), prompting Noah to call out Elle for not realizing Marco still has feelings for her. Encouraged by Chloe to talk to Elle, Noah quickly makes up with Elle. However, Marco, unwilling to give up, shows up to the Fourth of July party where he again fights with Noah and punches him, but Noah refuses to retaliate. Meanwhile Elle is also upset that Lee has found another guy, Ashton, who just finished his 1st year at Berkley and the 2 really hit it off and became best friends. Elle is upset for not being Lee's BFF anymore.Marco admits to Elle that he does still have feelings for her, but she's not interested. She goes off to find Noah, but Elle is unaware that Noah saw her acceptance letter to Berkeley. At the same time Elle struggles in accepting her father's new girlfriend, Linda, who tells her she was her mother's friend. She eventually understands and accepts her after her father tells how she and Brad (Carson White) had been his main focus for the last several years and that he deserves a chance in love as well. Noah's worried that she's only going to Harvard for him (as she has been ignoring Noah while she tries to complete the bucket list with Lee) and he doesn't want Elle to regret it if they later break up. Because of this, Noah breaks up with Elle and encourages her to make a college decision for herself.While dealing with the heartbreak, Elle misses a bucket list with Lee to play Dance Dance Revolution (just before the machine was to be removed forever). They clash when he tells her that he's never mattered to Elle compared to Noah, while she tells him to grow up and that all of her decisions this summer have been about trying to make everybody happy.Noah and Lee's mother tells Elle this much when she comforts her, telling her that she should start thinking about "what it is that you want to do" and choose a college based on that. It was also revealed that Noah and Lee's parents eventually decided to not sell the beach house (when they realize that the beach house means a lifetime of memories for the kids), and Rachel broke up with Lee, having seen the issues that Elle and Noah's relationship had, though she hopes they will reunite somehow. Marco apologizes to Elle, and they say their farewells amicably, before Elle reconciles with Lee and tells him that she's realized that she's spent so long maintaining her relationships with Noah and Lee that she hasn't worked out what makes her happy. She applies to University of Southern California (USC), in Game Design (she gets in after she pitches her idea for a fantasy sports league for e-sports). She tells the news to Lee, who is happy for her.Six years later, Elle is developing her own game. She and Lee remained close friends, both often visiting the fated Kissing Booth at the Charity Fair. Additionally, Lee and Rachel reunited with each other and got engaged after college. Sometime later, Elle sees Noah for (presumably) the first time since their breakup where he reveals he has job offers at law firms in Los Angeles and New York. He hasn't decided where he's going but does suggest going on a motorcycle ride when he's back in town. Noah says he will call Elle and she says she would like that. They part ways, but not before looking back each other - it is made clear they have never stopped loving each other.At the end of the movie, you see Elle and Noah riding down the coastline in California on their motorcycles, laughing and having fun, alluding that Noah chose the LA office and they rekindled their romance now that they have both grown up.