Lydia Quixano Perez runs a bookstore in the Mexican city of Acapulco until one violent day changes everything. Forced to flee, Lydia and her eight-year-old son, Luca, find themselves miles and worlds away from their comfortable middle-class existence. Instantly transformed into migrants, Lydia and Luca ride la bestia --- trains that make their way north toward the United States, which is the only place they might feel safe. As they join the countless people trying to reach el norte, Lydia soon sees that everyone is running from something. But what exactly are they running to?