Sean Vetter and his partner Demetrius Hicks came up on the mean streets of Los Angeles but now work together as DEA agents, fighting a seven-year war to stem the virulent drug pipeline along the US/Mexico border. Dubbed "the gunslingers" for their tough street tactics, their perseverance pays off when they take down notorious Baja Cartel kingpin Memo Lucero Geno. With Lucero locked away in a maximum-security prison, Vetter is finally able to go home to his wife, Stacy, a sanctuary from the harsh realities of his job. But in the wake of Lucero's arrest, a mysterious figure, known only as Diablo, emerges to violently claim the Baja Cartel. And when Vetter and Hicks set their sights on identifying and stopping this dangerous and elusive new player, Diablo makes the fight personal--robbing Vetter of the one person who gives his life meaning--Stacy. With nothing to lose, Vetter pulls out every hidden resource at his disposal to bring Diablo down--including an unlikely alliance with the jailed Cartel boss Lucero. He will stop at nothing to avenge his wife's murder, edging dangerously close to the line between justice and lawlessness, even if it sets him at odds with the police unit to which he has dedicated his life.