‘The Vow’ brings jaw-dropping detail to the strange story of NXIVM

In one of the key moments of “The Vow” — a stunning expose of the self-improvement group NXIVM and its downfall — filmmaker and former member Mark Vicente tells others seeking to break free that he’s “recording everything.”

That strategy pays off with intense, uncanny details about the inner workings of what prosecutors described as a secret sex cult, and a docuseries that plays like an espionage thriller.

Directors Jehane Noujaim and Karim Amer (“The Great Hack”) spent years chronicling the tale of NXIVM and its charismatic leader, Keith Raniere, whose hold was broken by a sex-trafficking case that implicated other members, among them former “Smallville” co-star Allison Mack and heiresses to the Bronfman family fortune.

NXIVM’s roots, however, go deeper than that, as Raniere charmed a variety of Hollywood figures, wealthy benefactors and even the Dalai Lama, with whom he’s shown meeting despite the spiritual leader’s caution about engaging with him.

There is, in fact, an almost surreal aspect to “The Vow,” which broadly illustrates people’s vulnerability to smooth-talking hucksters, and the way that Raniere’s organization insinuated itself into the lives of his true believers.

That buildup precedes laying bare a group within the group that pushed women into sexual relationships with Raniere and branded them — literally carving symbols into their skin — while setting up a system of “masters” and “slaves,” demanding “collateral” that would prove embarrassing to ensure the latter’s obedience and compliance.

Gradually, the web of those seeking to topple what they liken to a prison includes not only Vicente and his wife, Bonnie Piesse (who appeared in the “Star Wars” prequels), but actors Sarah Edmondson and former “Dynasty” star Catherine Oxenberg, who wages a different battle to extricate her daughter, India, from the group.

Along the way, viewers are treated to countless phone calls and videos, documenting each step as disenchanted members endeavor to break away in what feels like real time. That extraordinary access separates “The Vow” from other docuseries projects, since it doesn’t rely on the recollections of those involved but actually peers over their shoulders and listens in as much of the story unfolds.

The way NXIVM sought out and rubbed elbows with the rich and famous only heightens the sensation of watching a real-life soap opera, one whose over-the-top drama initially risks feeling too slick and massaged. Chalk that up, in part, to the abundance of performers featured, beginning with Raniere himself.

Soon enough, though, the narrative settles in as an eye-opening demonstration of how cults operate, transforming NXIVM’s Executive Success Programs, or ESP, into a near-religious crusade. Vicente’s extensive footage shows him being drawn into Raniere’s orbit as an ally and confidant, before Piesse’s misgivings became his own.

Raniere is awaiting sentencing after being found guilty of racketeering, sex trafficking and other crimes, but one can see the inordinate sway he wielded over followers, dispensing pearls of wisdom like, “A cynic is someone who seeks to turn good to bad.”

A cynic might also say the abundance of docuseries has diluted the genre’s impact, as has the tendency to drag multi-part projects out too long. For every zeitgeist-worthy “Tiger King” — which landed at just the right time — there are two or three you could easily do without.

“The Vow,” by contrast, plunges so deep into this bizarre world that it stands apart from the crowd. Even stretched to nine chapters, its immersive look into how cults can flourish delivers, in TV terms, a different kind of manual for success.

“The Vow” premieres Aug. 23 at 10 p.m. on HBO, which, like CNN, is a unit of WarnerMedia.