The novella follows 17-year-old Charlie Spring and his 18-year-old boyfriend, Nick Nelson, as they navigate the prospect of long distance when Nick leaves for university.
Charlie, the Head Boy (senior student leader) of Truham Grammar School, narrates the opening on the last day of school for Year 13, the final year of secondary education. Inside a cardboard fort the older students have built on the tennis courts, Charlie finds Nick, his boyfriend of two years, snapping photos with a disposable camera he bought to have prints for his university wall. Standing together, Charlie is struck by the realization that he is the one being left behind. He keeps this sadness to himself.
Nick, narrating his own chapters, admits he cried when the final bell rang. He is eager for independence at the University of Leeds but nervous about coming out as bisexual to new people, leaving his mum alone, and leaving Charlie. That afternoon the couple settles into their routine at Nick's house: video games, walks with the dogs, comfortable silence. Nick notes that Charlie has anorexia; though much improved after time in a psychiatric hospital the year they started dating, Charlie still never eats snacks, and Nick quietly makes a habit of always offering food. When Nick enthusiastically describes the Leeds rugby team, Charlie grows bored and cuts him off with a kiss, deflecting any talk of the future.
Charlie privately reveals the source of his anxiety. He has a large following on Tumblr, a social media platform, and after mentioning that he and Nick will be long distance, anonymous users flooded his inbox with warnings that such relationships always fail. The messages feed a fear he already carries. He and Nick discussed long distance once before, and Nick reassured him, but they have not revisited the topic. Charlie refuses to raise the issue because he does not want Nick to feel guilty.
The next day, Nick bombards Charlie with excited texts about university. At school, Charlie's friend Aled Last, a quiet classmate, asks what is wrong and reassures Charlie that a couple as solid as he and Nick will not break up. Charlie takes some comfort but retreats to the locker room, reads more discouraging anonymous messages, and deletes Tumblr from his phone.
That evening at a leavers' party, Charlie drinks heavily, flirts aggressively with Nick, then avoids him. Sitting drunk on the basement floor, he learns from Aled that their friends Tao Xu and Elle Argent, a couple together nearly as long as Nick and Charlie, have decided to break up rather than try long distance. If a devoted couple like Tao and Elle would give up, Charlie reasons, perhaps Nick secretly wants the same.
Nick finds Charlie crying and pulls him to the empty conservatory. Charlie, still drunk, stuns Nick by saying Nick is free to end the relationship. Nick interprets this as Charlie trying to break up but being too afraid to say it. Charlie erupts, shouting that he is the one getting left behind, that Nick talks about university as though it is the best thing that has ever happened to him, making Charlie feel like Nick cannot wait to get away. Nick fires back that Charlie cannot be angry at him for simply going to university. Charlie tells Nick to leave, and Nick storms out to his car, where he sits for 20 minutes hoping Charlie will follow. Charlie does not appear.
Charlie wakes the next morning hungover and filled with self-loathing. His older sister, Tori, hugs him while he cries and tells him firmly to talk to Nick. Nick spends the weekend in grief, crying himself to sleep and discovering he has lost his disposable camera. Neither one reaches out, and nine days pass in silence. Charlie throws himself into exam revision. Nick tells his mum that Charlie broke up with him.
Two weeks after the argument, Aled asks Charlie directly whether he and Nick have broken up. Charlie says yes for the first time, and the word shakes him. Aled challenges the assumption: Nick never said he wanted to break up, and if Nick believed Charlie was ending things, Nick would not have protested but would simply have been heartbroken. The logic gives Charlie hope.
At home, Tori produces Nick's disposable camera, found between sofa cushions. The film counter reads zero. Charlie takes the camera to a pharmacy for developing and, while waiting, receives a text from Tao: He and Elle have gotten back together, having realized their breakup was a mistake. Tao adds that he saw Nick leaving the party visibly upset.
Charlie flips through the developed photos on the bus home and discovers that the vast majority are of him: asleep in Nick's bed, on the laptop, with the dogs, on a hill, laughing, curled on the sofa. Nick spent an entire roll of film documenting their ordinary life because he wanted to remember it. Charlie tears up and sends Nick the silly selfie from the developed batch.
Over the next two days, Charlie sends every saved photo of them from his phone, but Nick's damaged phone cannot display picture messages, and every image arrives blank. Nick assumes it is a glitch and stops opening them. When Charlie tells Tori that Nick is not responding, she insists a physical gesture is needed. Charlie selects the photo of himself asleep in Nick's bed, writes on the back that he loves Nick, and asks Nick to meet at the local primary school's summer fete the next afternoon. Charlie posts the envelope through Nick's letterbox.
Nick comes home from an exam and finds the envelope. The next day he walks through the gate at the fete and faces Charlie for the first time in over two weeks. They sit on the asphalt scrolling through photos on Charlie's phone. Nick explains that his broken phone turned every picture message blank, which is why he never replied.
After a pause, Nick says he does not want to break up. Charlie, nearly crying, says the same. They exchange apologies: Nick for shouting and not driving Charlie home, Charlie for getting drunk and telling Nick to leave, Nick for talking about university constantly, Charlie for resenting it. Nick says he never wants to break up, and Charlie agrees. They kiss, and Charlie senses they have entered a new phase, stronger and more certain. Charlie gives Nick an Oreo Dairy Milk chocolate bar he bought. Nick jokes that they are practically married, then holds out a piece. Charlie, who never eats snacks because of his anorexia, surprises them both by saying yes.
They drive to their favorite beach, walk the shore, eat fish and chips, and watch the sunset. That night at Nick's house, they stay up talking honestly about what long distance will look like. Lying together at three in the morning, Nick says he loves Charlie more than anyone and wonders whether that is strange at eighteen. Charlie answers that he is weird too. The next morning, Nick convinces Charlie to skip school and stay in bed. Charlie agrees, a contented reversal of the routine they shared two weeks earlier.