Because of that chaos, it might have benefited from an indexed cast of characters. But Winslow can’t provide one. For one thing, it would be a spoiler. You just have to watch these miscreants as they drop. The Barrera heirs, would-be successors and arriviste rivals — a whole indulgent younger generation named Los Hijos, characterized by wretched excess and suicidal stupidity — make for countless shifting allegiances, fake names, dispensable henchmen and other complications.

Along with the battle to succeed Barrera, the plot involves Keller’s becoming head of the D.E.A. despite his strong distrust of the federal government and its approach to solving America’s drug problems. In order to do that, Keller sets himself up as a kind of independent investigator, which has a current resonance, too. The book makes Winslow’s clear case for why everything we’re told about Mexican drug imports is wrong: why New York is so vital to the country’s illegal-drug distribution, and even production; how Wall Street money and drug money are intertwined; and how money laundering intersects with businesses like real estate.

Enter Jason Lerner, a very Jared Kushner-like character, and his father-in-law, John Dennison. Dennison has Donald Trump’s history, speaks Trump’s own words and has a name that combines two sobriquets (John Barron and David Dennison) that Trump once used while pretending to be his own spokesman.

Winslow describes sting operations with immersive, heart-grabbing intensity. You don’t read these books; you live in them. You come to learn all about what it means for a good cop to go undercover as a bad one; for a black ex-con to be coaxed into the world of high-stakes New York drug dealing because he can reach a market Mexicans can’t; for a Staten Island addict to fall helpless prey to the drug trade’s latest bright idea (a near-lethal burst of fentanyl added to the usual heroin). Each story is personal. But each has huge ramifications in Winslow’s larger scheme.

The single most wrenching subplot involves a 10-year-old Guatemalan boy whose life is all but over, thanks to a system of graft that makes prostitutes out of women and thugs out of men. The boy is not described cheerlessly; Winslow doesn’t write in that register. The child is amazingly hardy. But the book shows the single day, the single stroke of fate, that may determine his entire future if the systemic corruption that pervades “The Border” has its way.

About making prostitutes out of women: Let’s just say that Winslow didn’t invent the horrors of the drug world, and assume he’s presenting a version of what he’s seen and heard about them. The words used around gender and race in this book are frequently ugly, and in these times that calls for a warning.

Last and never least with Winslow: the matter of languages. He is fluent in many of them, and “The Border” once again shows off those talents. There’s slang, of course. Why have a snitch sing when he can be “doing his best Freddie Mercury imitation for D.E.A. right now”? There is cop. There is politician, hit man, high roller. There is psycho — always a favorite, and always handy in the circles in which these books have traveled. “We’re soul mates,” one character says to another. “In the sense that neither of us has one.”

The border ends with another idea about the soul. “There is no wall that divides the human soul between its best impulses and its worst.” Two classic trilogies, “The Godfather” and now this one, are built upon it.