The first of the book's two prologues introduce the main characters, Aidan and Clare. They are high school sweethearts who have just graduated and are about to head off to separate colleges. Clare has made it clear to Aidan that this change of circumstances in their relationship will result in a secession of that relationship. They have just half a day left before both leave for college. Aidan reminds Clare that “A lot can happen in twelve hours.”
As it turns out in this particular case, that is not necessarily true. The story is divided into chapters representing various stops at various places which hold meaning to the past of the couple. The first stop occurs at 6:24 PM at the high school they attend and what happens here sets the stage for the repetitive quality of the various other stops to come. These stops at various places in the town are traveled to according to a list made by extreme list-maker Clare. Aidan suggests the stops represent a chronological scavenger hunt. Clare counters that it is more like a refresher course. The point is that each stop will be a place that holds meaning to the couple. The meaning of most places, however, are not particularly significant. For instance, the high school represents little more than a starting place that sets the template for each place to come. Clare tries to show Aidan that the time has come to put an end to the romance unless she decides that maybe he is right and they should continue long-distance. For Aidan, each stop represents another chance to prove that the romance is not yet ready to be trashed simply because intimacy will no longer involve tactile connection.
From the school, the couple travel to a pizza joint and then to the beach. At both spots they discuss their past, the current state of their relationship, and whether it is worth continuing over the distance between their respective institutions of higher learning. Clare expresses doubt and demonstrates an inability to make a concrete final decision. A stop at the Gallaghers' house is made to pick up Aidan's brother Ricky and drop him off at the bowling alley. Clare admits that the bowling alley is on the list, but it is not next. This turns out to be of little consequence as Clare quickly agrees to switch its place within the chronology and so the next stop does turn out to be the IncrediBowl which is notable for a decor that is substantially out of sync with the time. The symbolism relative to the future of Aidan and Clare is made clear.
A min-mart and a fountain precede a stop at a party being held at Andy Kimball's house. Inside, Aidan and a boy named Scotty get into a violent fight. When Scotty blames the fight on Clare's hot-headed boyfriend, Aidan is motivated by the look on her face to confess that he is not her boyfriend anymore. Everyone sort of toasts to the party being the end of an era. They leave the party, discuss what the fight was about, and have a longer discussion about how the plans for following Clare's list went off-track. Then they find a place to dance and come to a seemingly final decision about breaking up for good. Shortly after that, they receive news that Scotty is jail and rush to the police station.
At the police station there is more discussion about the future and Clare's uncertainty about what awaits. The next stop is the home of Scotty's parents who are themselves not at home. Scotty's girlfriend Stella mentions that Clare put together a scavenger list to "decide the fate of her relationship." Clare denies it is a scavenger hunt. After deciding, on Scotty's driveway, that the evening has reached another point at which there is "another ending" she and Aidan head for Clare's home. It is now 2:41 in the morning and they make their way to the basement of Clare's home. The basement brings up memories of physical intimacy. A discussion of who was obsessed with whom eventually turns into a game of ping-pong which becomes a symbol of the entire narrative. The two players slap a ball back and forth without any intention to score a point, but merely for the pleasure of seeing how long they can keep a rally going. It becomes a metaphor for their relationship and the whole point of all the stops on this last night together.
It is nearly four in the morning when they head for the next stop on the list: the lake. It is far too cold to go for a swim, but that is not going to stop Aidan. He disappears into the frigid lake and eventually Clare reaches the point of terrorized anxiety that drives her into the water to find him and, if necessary, save him from his crazed impulsiveness. Clare tells him she loves him. He mishears as "I dove you." She says it again and he says it back.
Just before 5:00 AM the couple make their way back to the Gallagher home where they change out of their clothes and put something warm on to stem the coldness of the lake. Aidan's dad tells a story about how he and Aidan's mom lived through a rough patch of long-distance relationship status when he was in the navy. He then asks if the two are planning on staying together as a couple. Aidan tersely answers "No." Clare, ever unable to fully commit to a decision, is knocked for a loop by Aidan's decisiveness for her. Inside the car, however, there is one last long discussion about whether they should continue as a long-distance couple or just call it quits. The final stop is metaphorically subtitled "The End." After twelve hours of questioning and debating and agreeing and disagreeing, they finally head off to their respective colleges alone.
The final prologue, which is really an epilogue, explains how Clare returns home over Christmas whereas Aidan stays in California because of the longer distance. At the post office, she finds she has been sent a square box with something very heavy inside. She opens it up to find a green bowling ball inside and a note with just four letters written on it: "Is it later yet?"
