Return to Sender by Julia Alvarez begins on a dairy farm owned by the Tyler family in Vermont. After an accident leaves Mr. Tyler incapacitated, the family finds themselves in dire straits, struggling to keep their farm afloat. In response to their predicament, they decide to hire laborers from Mexico. Among these is the Cruz family, who are undocumented immigrants. This new arrangement brings two young characters into focus – Tyler, Mr. Tyler's son, and Mari, the daughter of the Cruz family's patriarch.
Tyler is an empathetic and thoughtful boy. Although initially uncomfortable about the legal status of their new workers, he gradually befriends Mari and her two younger sisters, Luby and Ofie. He becomes privy to their struggles and their fear of being discovered and deported.
Mari, on the other hand, is depicted as a strong and intelligent girl. She frequently pens letters to her mother, who was deported after attempting to cross the border again after visiting her sick mother in Mexico. Mari longs for her mother and fears that their family could be separated at any time by immigration authorities.
Meanwhile, Mari's father, Papi, falls seriously ill from a stroke. As his condition deteriorates, Mari's uncle sends a letter to her mother about their dire situation. This prompts her mother to make another dangerous journey back to the United States.
The story reaches a climax when an unexpected turn of events occurs. Mari and her sisters are caught in a sudden snowstorm during a school trip. Tyler, who is on the same trip, helps them to survive until help arrives. This event draws attention to the girls, raising concerns about their legal status.
Amidst all this, Mari's mother finally returns, only to be arrested by immigration officers shortly after. Devastated but resilient, Mari decides to return to Mexico with her mother. Ultimately, the Tylers agree to legally adopt Luby and Ofie, allowing them to remain in the U.S. and offering them a stable future.
Return to Sender concludes with a sense of hope and bittersweetness. Though they miss Mari, Luby, and Ofie, Tyler and his family keep the farm going with the help of new workers. While facing an uncertain future in Mexico, Mari and her mother carry the strength of their experiences with them. Despite the odds, the bond between Tyler and Mari's families endures, embodying the potential for understanding, compassion, and unity amidst complex societal issues.