Cora is a twelve-year-old seventh-grade student who loves the logic and organization of math and science. She is struggling with profound grief after her older sister died in a school shooting the previous year. As a coping mechanism, she begins researching theoretical physics and wormholes, hoping to turn back time. She is also beginning to explore her Lebanese heritage with her father.

Quinn is a seventh-grader who lives next door to the Hamed family. Once an avid soccer player and artist, she has become a social outcast, isolated by the horrific actions of her older brother. Desperate to fix the past, she seeks out her former best friend with a plan to time travel and undo the tragedy.

Mabel is Cora's older sister who died at age fourteen in a school shooting. Before the tragedy, she was experiencing typical teenage milestones, such as experimenting with makeup and developing crushes on her classmates. Her death leaves a massive emotional void in the Hamed household.

Parker is Quinn's older brother who died by suicide after perpetrating a deadly school shooting. Before the tragedy, he became increasingly withdrawn, angry, and radicalized by hateful online forums. His violent actions irreparably damage his family and the surrounding community.

Mr. Hamed is a Lebanese immigrant and biology professor at the local university. He raises Cora with the help of his mother-in-law while privately managing his own intense grief over his eldest daughter's death. He remains gentle, supportive, and willing to have difficult conversations with his surviving daughter.

Grams is Cora and Mabel's maternal grandmother who helps raise Cora after her mother left the family. She takes a practical, straightforward approach to parenting. She encourages Cora to engage with her feelings and directly addresses Cora's avoidance of Quinn.

Mrs. McCauley is Quinn and Parker's mother. Following the shooting, she quit her job and channels her nervous energy into elaborate cooking projects. She actively avoids difficult conversations about her son's actions and frequently argues with her husband over who is at fault.

Mr. McCauley is Quinn's father. He immerses himself in long hours at work following his son's violent acts. He struggles to communicate with his daughter about the tragedy, preferring the idea of relocating over confronting the painful reality of what happened in their home.

Mia is a classmate who grows closer to Cora after the shooting. She participates in the Junior Quiz Bowl team and is highly protective of Cora. She frequently expresses jealousy when Quinn attempts to reenter Cora's life.

Owen is a Japanese American classmate and a member of the Junior Quiz Bowl team. He has been friends with Cora since the second grade and becomes the subject of her first romantic crush. He is polite, thoughtful, and tries to ease tensions within their friend group.

Dr. Randall is Cora's therapist. He works with her to process the trauma of the school shooting and guides her as the anniversary of Mabel's death approaches.

Mrs. Euclid is a teacher at the middle school. She tries to provide a supportive environment for Quinn and encourages her to speak to a professional about her emotional burdens.

Ainsley is Quinn's former soccer teammate. She checks in on Quinn and expresses how much the soccer team misses her participation since she quit.