Jam, a 15-year-old Black transgender girl, lives with her family in the town of Lucille sometime in the future. Decades before the start of the novel, angels defeated monsters in a revolution that began in Lucille and created a utopia. Neither monsters nor angels are supernatural beings; these terms refer to good and evil humans. The angels banned guns, abolished prisons, prosecuted corrupt and murderous police offers, and rebuilt institutions. The first chapter of Pet details the accomplishments of the revolution and pays homage to the countless people who died because of societal inequity or cruelty before the revolution: the people without access to health care, people killed in wars or natural disasters.

Jam signs to her teachers while at school. She asks about traditional religious understandings of angels. When the teachers encourage Jam to look up answers at the library, she is irritated by their lack of an answer. Jam takes out books from the library on religious interpretations of angels on her way home.

Jam’s mother, Bitter, is an artist and one of the only people that Jam speaks to verbally. Jam asks her mother about the angels and monsters of yore.