In her journal, sixteen-year-old Miranda Evans is counting down until her sophomore year of high school ends and summer vacation begins, but in the meantime she has tests, fights with her mom, and friendship drama. She first hears that a large asteroid is going to hit the moon from her mom’s boyfriend, Peter, but soon it’s all the newscasters talk about, and her teachers too—they use it as an excuse to assign moon-themed projects.
Despite the extra schoolwork, the mood is festive on the night the asteroid is supposed to hit. People in New York are having rooftop viewing parties, and even on Miranda’s rural Pennsylvania street, all the neighbors are out in an impromptu block party. Despite her older brother Matt’s misgivings about the event—which he had called home from college the night before to share—Miranda joins in the excitement with her mom Laura and younger brother Jonny.
When the asteroid first appears in the sky, however, the mood quickly changes to one of panic. The asteroid is denser than scientists had predicted and the collision knocks the moon off kilter, forcing it closer to Earth. The impacts are immediate, even if Miranda doesn’t know the full extent of them because cell service and cable channels stop working.
By the next morning Miranda has ascertained that her father Hal and pregnant stepmother Lisa, as well as her Grandma and Matt, are all okay. The world as a whole, however, is not. Due to sudden unpredictable tides and tsunamis, there were massive casualties on both coasts of the United States. Countries around the world with coastlines are devastated by the impact of the moon’s increased gravitational pull on their tides. Millions are dead.
Laura reacts to this news and the powerful electrical storms of the next day by pulling Miranda and Jonny from school and having them join her and their elderly neighbor Mrs. Nesbitt on a high-stakes shopping spree, where they buy nonperishable items and plants for a vegetable garden. Looking at their full pantry, Miranda tells herself that these precautions are ludicrous and unnecessary.
But in the weeks that follow, electricity continues to be unreliable, gas prices skyrocket, and the grocery stores remain bare. By the time Matt returns home from college and the school year ends, food shortages have become severe enough that classmates squabble over who will get Miranda’s friend Megan’s lunchtime peanut butter sandwich. Megan, like other congregants at the local Reverend Marshall’s church, has decided to fast and pray in response to the disasters.
Instead of things going back to normal, the outages escalate—as do the temperatures and the incidents of rare illness. The tides and tsunamis also haven’t stopped, and one morning Miranda wakes up to a grim, gray sky—the result of the ash cloud from dramatic worldwide volcanic eruptions.
Within days the temperatures plummet, and the vegetables in Laura’s garden begin to wither from lack of sunlight. Miranda had been making trips to swim at Miller’s Pond and meet up with Dan, a boy she’s started to see, but it’s soon too cold. By early August there is frost, and many people—including Hal, the pregnant Lisa, Dan, and Miranda’s friend Sammi, who is dating a forty-year-old man with resources and connections—leave their homes in the hopes of finding better conditions elsewhere in the country.
Miranda, Matt, and Laura all cut back to two meals a day, then decide to skip an additional meal every other day. They don’t share this plan with Jonny, however, because at thirteen years old, they think he’s too young to cut back more on meals. And, Miranda realizes, he is the one her mother is betting on to survive if they can’t all make it. She resents her mother for this, despite the fact that Laura is eating even less than the amount they agreed upon.
When their heating oil runs out the Evanses move into their sunroom, which has a wood stove. Miranda chafes under the lack of privacy and continued lack of food. A pair of old cross country skis is found in the attic and Matt, Jonny, and Miranda all take turns training on them. Laura, who has limited mobility due to a twice-sprained ankle, does not. Matt and Miranda discuss how the last person alive will use them to leave.
When Jonny, Laura, and Matt all begin to run fevers and are too weak to leave their mattresses, Miranda skis to the hospital for help. The building is deserted except for two nurses who explain that everyone else is dead—including Peter, Laura’s boyfriend. Miranda adds him to the list of deaths she’s endured, which now includes Mrs. Nesbitt and her friend Megan, who chose to starve to death as a sign of her religious faith.
Slowly, under Miranda’s care, Jonny and Laura recover. Matt does too, but he seems permanently weakened, and they fear that he strained his heart helping Miranda care for the other two while still sick.
In late February electricity begins to reappear sporadically for a few minutes at a time. The news reports are still much the same: lists of the dead, natural disasters, famines, droughts, and illnesses. In mid-March, with food supplies dangerously low, Miranda realizes that her whole family is not going to survive, and they can all starve to death slowly, or she can give Matt and Jonny a fighting chance.
In order to spare her mother from having to witness her death, Miranda walks into town—knowing that she does not have the strength to make the return trip. However, when she sits down on one of the deserted streets, she glimpses a yellow flyer. She hasn’t seen anything bright-colored in so long that she musters the energy to get up and capture it. The flyer directs her to City Hall, where food distribution had begun a few weeks ago. Miranda is driven home with four bags of groceries, and with the promise of more bags to come every week.
The novel ends on Miranda’s birthday, with her celebrating the fact that there’s food in the pantry, her family is alive and together, and with the hopeful assertion that she’s writing this journal not to chronicle her life for those who outlive her, but for herself, for a time when things look better than they are now.