Blood Daughters by Marcos M. Villatoro

A child dies on the border between California and Mexico. This is nothing new: immigrants die crossing the border all the time, escaping from poverty and violence in Latin America. They bake in the desert. But this death is different. Someone has taken body parts from the child.

FBI agent Romilia Chacón, a Salvadoran American, follows this case into a world that swallows her with its horror, a world that exists alongside ours, where children are bought and sold like cattle and shipped to men all across the country. The dealers in this blackest of markets have no moral barometer, only the lust for cash. And one among them has taken murder to a level beyond serial killing.

Romilia comes to this case already broken: the man she loved and yet had to hunt—drug runner Tekún Umán, a regular on the FBI's Most Wanted List—is gone. Romilia has two friends, her partner Nancy Pearl—who lives a double life between the Feds and the cartels—and a bottle of booze. Romilia's mother is on her back to get sober; her son drifts further away. And the killer is taking away pieces of Romilia's life, day by day.