Summarize the section titled, The Missing.

The novel begins with a section entitled "The Missing," which place in San Salvador's Instituto de Medicina Legal. There corpses and skeletal remains from the country's history of civil war and gang violence are being examined. In Chapter 1, readers are introduced to the Flores family and the struggles they have faced as poor rural farmers living in a country torn apart by gang violence. The twins' elder brother Wilber Jr. decided to go to the United States as an undocumented immigrant. After arriving in the United States, Wilber Jr.'s contact with his family became increasingly infrequent.