The Mother is a political journalist and sound documentarian who recently completed a collaborative project recording the atmospheric noises of New York City. She volunteers as a Spanish-language translator in a federal immigration court, where she becomes personally invested in the stories of refugees crossing the border. Struggling with a growing emotional distance in her marriage, she uses literature and audio recordings to process her environment. She possesses strong political principles and worries continuously about the ethics of using others' suffering for art.

The Father is a sound documentarist who prefers a conceptual, impressionistic approach to his work over journalistic literalism. Passionate about Apache history, he spends long hours studying maps and plans to record an "Inventory of Echoes" in spaces significant to Native American history. He remains heavily guarded about his creative intentions, often working in isolation, which contributes to the strain in his marriage.

The Boy is a ten-year-old child from his father's previous marriage who possesses a serious, articulate, and highly observant nature. Gifted a Polaroid camera for his birthday, he documents their cross-country trip and attempts to emulate both his parents' professional styles. As the family drives toward Arizona, he acts as a linguistic and emotional translator between the adult world of his parents and the child world of his younger sister.

The Girl is the five-year-old biological daughter of the Mother from a previous marriage. Playful and inventive, she possesses a unique ability to create new words and build a distinct family lexicon through her innocent misunderstandings. She functions as a hub for intellectual connection within the family, constantly asking questions that demand thoughtful answers from her parents and stepbrother.

Manuela is an undocumented woman living in New York City who speaks a rare native Mexican language. She illegally crossed the border from Mexico and later hired a guide to bring her two young daughters to the United States. She approaches the Mother for help translating legal paperwork when her daughters are detained by Border Patrol.

The Lost Children represent a collective identity throughout the narrative, initially referring to real-life migrant refugees crossing the border. As the family travels, the boy and girl adopt these figures into their backseat roleplaying games, blending news reports with fictional characters from a novel the Mother reads. The term expands to encompass various displaced youth in both reality and imagination.

Manuela's young daughters are traveling to New York City under the guidance of a hired guide. Their grandmother sewed Manuela's phone number into the collars of their dresses so they could contact her upon arriving in the United States. They become detained in a border facility and subsequently go missing, sparking the Mother's urgent search.

A priest who protests against deportation practices outside the federal immigration court. He explains the grim reality of daily federal quotas for migrant detention centers and leads demonstrations where people shout the names of missing relatives.