Mariana uncovers a lethal supply chain of American firearms being smuggled into the hands of drug cartels and fueling record levels of gun violence in Mexico. A journey filled with jaw-dropping access to gunrunners, mules, cartel bosses and assassins takes an even more terrifying turn when the son of the world's most notorious drug lord, El Chapo Guzman, is arrested and the cartel that Mariana infiltrates decides to violently revolt.