Miranda is a 16-year-old high school student and figure skating enthusiast living in Pennsylvania. She begins the story focused on typical teenage concerns, such as friends, boys, and arguments with her mother. As catastrophic global events unfold, she records her experiences, fears, and observations in her diary. She serves as the sole narrator of the family's changing reality.

Laura is Miranda, Matt, and Jonny's single mother and a professional writer. When news of the catastrophic moon event breaks, she immediately shifts into a pragmatic survival mode. She pulls her children out of school to frantically stockpile groceries, winter clothing, and supplies. She serves as the strict but necessary architect of her family's safety protocols.

Matt is Miranda's 19-year-old older brother, a pragmatic college student who studies philosophy. He returns home to Pennsylvania to help his family weather the crisis. He serves as a steadying presence in the household, working closely with his mother to chop wood, ration supplies, and maintain physical security around their property.

Jonny is Miranda's 13-year-old younger brother, a passionate baseball fan who dreams of playing professionally. As the youngest member of the family, he is often the focus of their protective instincts. He attends a local baseball camp early in the summer, which provides him with consistent meals while the rest of the family quietly rations their own food for his benefit.

Miranda's father and Laura's ex-husband. He lives in Springfield with his pregnant new wife, Lisa. He maintains contact with his children as long as the phone lines work and attempts to secure provisions for his growing family on the road.

Mrs. Nesbitt is an elderly neighbor and long-time friend to Miranda's family, having known Miranda's grandparents. She joins Laura and the children on their initial, chaotic grocery run and remains a close confidante to the family as conditions worsen.

Peter Elliott is a local doctor who is dating Laura. As a medical professional, he becomes overwhelmed with work after the asteroid strike. He visits the family when he can, providing them with critical medical advice regarding the spread of mosquito-borne illnesses and basic supplies.

Megan is one of Miranda's best friends. Following the death of their mutual friend Becky, she becomes highly devout. In the wake of the global disasters, she views the events as divine punishment and begins severely restricting her own food intake as an act of religious martyrdom, deeply frustrating Miranda.

Sammi is another of Miranda's closest friends. She reacts to the stress of their friend Becky's death and the subsequent global disasters by seeking out older romantic partners. She eventually plans to leave town with a 40-year-old man in hopes of finding better living conditions elsewhere.

Miranda's father's second wife. She is pregnant when the asteroid hits, making her highly vulnerable in the rapidly deteriorating world. She travels with her husband to check on her own parents.

Dan is a teenage boy who shares a mutual attraction with Miranda. They spend time together at a local swimming hole, offering each other a brief sense of normalcy and teenage romance before his family decides to leave town.

Brandon is a local professional figure skater and Olympic hopeful. Miranda idolizes him, and he later serves as a symbol of hope and continuity when she unexpectedly runs into him skating at Miller's Pond.

Reverend Marshall is the leader of Megan's church. He encourages his congregation's extreme religious fasting and views the disaster as a divine test.

Mrs. Wayne is Megan's mother. She watches helplessly as her daughter slides into extreme religious asceticism as the world's food supplies dwindle.

Becky is a close friend of Miranda, Megan, and Sammi who died prior to the events of the novel. Her death deeply affected the remaining friends, altering their personalities and permanently shifting their social dynamics.

George is a 40-year-old man who begins dating Sammi after the disaster strikes. He provides food to Sammi's family and offers her an opportunity to travel with him to find better living conditions.