American Dirt by Jeanine Cummins

From number one New York times bestseller.
Lydia Quixano Pérez lives in the Mexican city of Acapulco. She runs a bookstore. She has a son, Luca, the love of her life, and a wonderful husband who is a journalist. And while there are cracks beginning to show in Acapulco because of the drug cartels, her life is, by and large, fairly comfortable.
Even though she knows they’ll never sell, Lydia stocks some of her all-time favorite books in her store. And then one day a man enters the shop to browse and comes up to the register with a few books he would like to buy—two of them her favorites. Javier is erudite. He is charming. And, unbeknownst to Lydia, he is the jefe of the newest drug cartel that has gruesomely taken over the city. When Lydia’s husband’s tell-all profile of Javier is published, none of their lives will ever be the same.
Forced to flee, Lydia and eight-year-old Luca soon 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 Javier’s reach doesn’t extend. 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?