It is Cora Hamed’s 12th birthday. Cora loves math because it is logical and makes sense to her. Cora goes to Pete’s, a local pizza shop, with her grandmother, Grams, and her father to celebrate. This is a family tradition, although it feels different without Cora’s older sister, Mabel, who was killed the previous school year. Cora thinks about how certain numbers are added to make 12 and how she will eventually be older than Mabel. Mabel was 14 years old when she died.

Quinn McCauley, the girl who lives next door, leaves a present for Cora on their stoop. Cora is no longer friends with Quinn. Cora’s father urges Cora to remain friendly with Quinn, but Cora is reluctant. She privately suspects that her sister, Mabel, would have expected her to hold a grudge against the McCauley family.

In a note to her brother, Parker, Quinn remembers a time Parker cried after helping her down from a tree. Quinn reflects that she hasn’t heard back from Cora about the box that she left on her stoop three days earlier on Cora’s birthday.

At school, Quinn goes to the library, a place where she spends a lot of her time.