Belly Conklin has grown up with Conrad and Jeremiah Fisher. Her mom, Laurel, and their mom, Susannah, were lifelong best friends, so Belly, her mom and her older brother, Steven, have spent every summer at Susannah’s house in Cousins Beach.
But this summer, everything is different. Susannah died of cancer in May, leaving all her friends and family grieving. Belly feels like she has lost the whole Fisher family, not just Susannah, since she has scarcely spoken to Jeremiah since the funeral and her relationship with her former boyfriend, Conrad, is even more strained.
Belly has been in love with Conrad since she was a child. They finally established a romantic relationship the previous summer, but the two exchanged harsh words at Susannah’s funeral. Belly recalls that the beach house was full of people after the funeral, and when Belly went to find Conrad, he was in the basement resting his head on a girl’s lap.
The girl was Conrad’s ex-girlfriend Aubrey, and even though Belly and Conrad had already ended their romantic connection, the sight of him being comforted by another girl drove her into a fit of jealousy. Conrad told Belly to grow up, and she cursed at him. Then he said he was wrong to ever start a romance with her because she’s so childish. She said that she hated him, and the two parted ways on bad terms.
In July, Belly is still mourning Susannah’s loss and going through the motions of normal life. But then she gets a call from Jeremiah. Conrad has skipped his summer classes and has been missing from college for two days. Jeremiah wants Belly to come on a road trip to help him find Conrad. Belly agrees.
In Jeremiah’s point of view, he recalls how much Belly had changed the previous summer. She arrived at the summerhouse suddenly mature and beautiful, and he began to see her in a romantic light, even though she only had eyes for Conrad. He felt resentful that she would choose Conrad over him and even more jealous of the fact that, after years of ignoring her, Conrad suddenly showed an interest in Belly.
Belly lies and tells her mother that she’ll be staying at her best friend Taylor’s house for a day or two. Jeremiah picks her up, and they drive toward Conrad’s college to question his roommate about Conrad’s disappearance. Jeremiah mentions that Belly’s prom photos with Conrad looked good.
Belly wonders how Jeremiah knew that Conrad drove down from college to attend prom with her the previous spring. This causes Belly to remember her disastrous prom with Conrad. She had to pressure him into attending it with her, he looked miserable the whole time, and he would barely dance or make conversation or do any of the fun romantic prom activities she’d dreamed about. He was emotionally distant. Belly realized that he only attended her prom because his mother wanted him to. Heartbroken, Belly had told Conrad their relationship was over.
At Conrad’s university, they learn that he has gone to the beach house. There’s a sense of urgency to find him. If he misses his Monday exams, he’ll fail his summer term.
Belly recalls the previous Christmas when Conrad had driven for hours just to see her. He pulled up outside her house at midnight, and she ran out to join him in the car. He drove her out to the beach house in Cousins Beach, and they stayed overnight. Even though they only kissed, it was the most romantic night of Belly’s life.
Jeremiah and Belly arrive at the beach house, where they attempt to convince Conrad to return to school. He insists that he’s not leaving the beach house. Belly and Jeremiah stay the night so that they can continue their persuasion the next day.
Even though her interaction with Conrad is tense and unfriendly, Belly is thrilled to be back at the beach house where she made so many childhood memories. The next day, Mr. Fisher’s real estate agent visits the house. When Conrad sends the woman away and informs her that the house isn’t going to be put up for sale after all, Belly realizes that Conrad didn’t come to the summerhouse to skip his exams and escape his problems. Instead, he came to save his mother’s favorite place from being sold by his out-of-touch father.
Mr. Fisher comes to the house to talk to Conrad, who refuses to accept his father’s plan to get rid of the beach house. Mr. Fisher leaves after declaring that the house will be sold no matter how much Conrad opposes the idea. Jeremiah decides that if it’s his last night at the beach house, he’s going to buy alcohol and throw a party. Pre-party, Jeremiah and Belly drink some alcohol, and he dares her to kiss him. He’s openly disappointed when she only kisses him on the cheek.
People start arriving for the party, and Belly begins drinking more. Jeremiah and Belly want to swim in the ocean, but Conrad forbids it, saying that Belly is drunk. Angry with Conrad, Belly runs out of the house and toward the ocean. When Conrad comes after her, she grabs a bottle of tequila from his hand and drinks directly from it.
She dares him to stop her from swimming. When he picks her up and carries her away from the ocean, she yells at him and demands to be put down. He drops her in the sand, and she cries and apologizes for treating him badly on the day of his mother’s funeral.
Conrad forgives her, and she goes back to the house. Completely drunk and heartbroken that Conrad hasn’t decided to restart a romantic relationship with her, Belly calls her mom, Laurel, and asks for her help in stopping Mr. Fisher from selling the house.
When Belly goes upstairs to sleep after everyone leaves the party, Jeremiah asks Conrad if he still likes Belly. Before Conrad can reply, Jeremiah says that he himself truly likes Belly, which prompts Conrad to say that he doesn’t like her and only took her to her prom because she asked him.
The next morning, Laurel arrives at the beach house, and she is furious that Belly lied about staying at Taylor’s house. Laurel says they have to leave, but Belly adamantly refuses and wants to save Susannah’s house. She says she wishes Susannah was her mother instead of Laurel and says Susannah would never forgive Laurel for letting the Fisher boys lose their beach house.
Laurel slaps Belly after the last remark. She then apologizes for the slap and for being an absent parent in Belly’s life due to her grief over losing Susannah. Laurel promises to fight for the house on the boys’ behalf.
Laurel invites Mr. Fisher to the beach house and convinces him to leave the house for the boys to enjoy. Mr. Fisher’s one condition to not selling the house is that Conrad must return to summer school and pass all his final exams.
Belly sets up a study area at the beach house, and she and Jeremiah help Conrad study all night. The next morning, Conrad, Jeremiah and Belly drive away from the beach house, and Belly cries because leaving the house feels like losing Susannah all over again.
They drive to Conrad’s university, and Belly and Jeremiah have a heart-to-heart talk while Conrad takes his exams. Jeremiah wonders why Belly never came to visit him after his mother’s funeral. She apologizes and says she should have come. Belly asks Jeremiah if Conrad ever misses her or talks about her. Jeremiah gets so frustrated by her ongoing attachment to Conrad that he kisses her. He confirms that he still likes her, and Belly kisses him back.
Conrad finishes his last exam and finds his brother and Belly kissing in the car. When he runs away angrily, Belly runs after him. She and Conrad exchange some tense words, but even though he’s jealous, he won’t actually say that he loves her. Belly realizes that she should choose the brother who will say what he really thinks instead of always hiding his true feelings. Conrad tells her that he never wanted her.
That evening, the three of them drive toward Belly’s home in silence. A severe rainstorm forces them to pull over at a hotel and stay the night. Jeremiah falls asleep right away, and Conrad whispers to Belly that he was lying about never wanting her. He falls asleep, and the next morning when Belly wakes up, he tells her that a friend is coming to pick him up at the hotel and that Jeremiah will drive her home.
Belly realizes that this is finally the end for them and that Conrad will never express love for her in the way she wants. As Jeremiah drives Belly home, she holds his hand and feels happy and content with her choice.