Have you given thanks for your BS detector lately? Has it served you well during this dire age of disinformation? Lately I find myself grateful for whatever is left of mine, honed by a lifetime of being told I have an attitude problem, give off “negative energy” or ask too many questions.

Which leads me, with authentic enthusiasm, to applaud filmmakers Jehane Noujaim and Karim Amer for their thoroughly absorbing HBO documentary series, “The Vow,” an elliptical and haunting journey into the dark heart of a self-help group known as NXIVM (pronounced “nexium”), that was exposed in 2017 as both a cult and a pyramid scheme.

Some of the women drawn into NXIVM’s elite circles have described coerced sex, vigilance over their diets and daily routines, blackmailing schemes and secret branding ceremonies at which the initials of NXIVM’s founder and self-anointed guru (a remarkably influential little creep named Keith Raniere) were seared on their private areas. Former acolytes talk about how Raniere and NXIVM tried to sue them into oblivion after they left the group, among other intimidation tactics. Still others talk about a broader realization: They’d joined a cult and didn’t know it until they were too far in.

“The Vow,” which premiered in August and concludes this Sunday (and is available for streaming on HBO Max), may well be this dreadful year’s most vital and relevant documentary, and that’s saying a lot, as I’m currently drowning in top-notch documentaries about voter suppression, Russian hacking, White House corruption, racist policing, a dying planet and culture clashes of every kind — all of which have aired or will air before this apocalyptically approaching Election Day. Strong as they are, most of them will only be viewed by people who’ve already heard the alarm bells.

“The Vow,” however, strikes a rawer nerve. On its face, it’s just another story of how badly people can be deceived, especially when they lack self-confidence or an ability to smell a steaming pile. Sympathy for suckers is in short supply these days, especially as one realizes that NXIVM thrived by preying on a privileged class of mostly well-off, mostly White people, many of them trying to make it in Hollywood.

To watch “The Vow” is to recognize how faulty our personal radars have become, no thanks to four-plus years of political gaslighting. The other day I nearly failed an online quiz that asks you to spot fake-news postings on social media. I correctly identified seven and missed three. It was chilling.

NXIVM, which at its core was a twisted kind of multilevel marketing scheme, isn’t all that different from QAnon’s Facebook presence or the anti-vaccine movement; Trump University or Vladimir Putin’s robo-network of online infiltrators. You may not be in danger of joining a sex cult or spreading a conspiracy theory, but what about that old friend who is still trying to sell you a lifetime supply of essential oils? What about those scam calls asking for your Apple ID, from unlisted numbers you can somehow never block?

In other words, how’s your BS detector holding up these days?

That’s what “The Vow” is really about.

Aided by NXIVM’s thoroughly modern impulse to record everything it did for 20 years (creating a trove of revealing phone calls, videos and manifestos), Noujaim and Amer ingeniously begin their documentary by immersing the viewer in the world of NXIVM’s gateway outfit, Executive Success Programs (ESP). This mirrors Noujaim’s own experience — she took an ESP self-improvement course more than a decade ago after enthusiastic recommendations from heiress Sara Bronfman and NXIVM executive Mark Vicente, a filmmaker who co-directed the 2004 pseudoscience documentary “What the Bleep Do We Know!?”

As Noujaim told the Los Angeles Times, she dropped out before completing the course. After completing it years later, she learned that Vicente and his actress wife, Bonnie Piesse (who played Luke Skywalker’s future aunt in the Star Wars prequels), had abruptly left NXIVM.

Another defector was Sarah Edmondson, a TV and film actress who had risen through NXIVM’s intricate levels and ran the group’s Vancouver outpost, and Edmondson’s husband, Anthony “Nippy” Ames, an actor and former collegiate football player who helped found NXIVM’s all-male support group, called the Society of Protectors.

Noujaim and Amer, who are married, decided to follow the former members through their efforts to expose NXIVM as a criminal enterprise. They are joined by actress Catherine Oxenberg (you may remember her from the original “Dynasty” series), who is desperate to get her daughter, India, out of NXIVM’s grip.

The people viewers first meet in "The Vow" exude a nebulous happiness when describing the program, which, frankly, resembles a lot of corporate team-building BS — helpful to some, hokey to others, but mainly harmless psychobabble about subconscious intentions and fixing the habits that hold us back from achieving our goals.

By “The Vow’s” second episode, it’s clear that the glow they were experiencing was filmed before the organization erupted in scandals that eventually led to an FBI investigation and the arrests of Raniere and several others. The enlightenment was all bogus; some followers paid six-figure sums to work their way through the ESP levels, awarded with color-coded scarves to wear at group meetings. The main goal was to recruit others, in the classic scam formation of superiors and underlings.

Along the way, we learn how Raniere (who awaits sentencing this month on federal convictions of sex trafficking, sexual exploitation of a child, racketeering and wire fraud, among other crimes) manipulated his most fervent followers. At one point, NXIVM membership reached a reported 16,000.

Some viewers and critics have found “The Vow” to be protracted and tedious at nine (often confounding) episodes, wishing that it would more quickly get to the lurid accounts of what went on. The saga has certainly provided plenty of fodder for in-depth journalism, a memoir (by Edmondson) and other formats. Another docuseries, “Seduced: Inside the NXIVM Cult” premieres Sunday on Starz and focuses on Catherine and India Oxenberg’s story; as possible as it seems that this story has been milked for all its worth, Sunday’s finale of “The Vow” delivers a swerve at the very end that suggests there may be more to come.

The series succeeds on the looping, empathetic nature of Noujaim and Amer’s approach — a layered reveal that speaks to anyone who ever had to hear (or ever was the one to say) that there’s no “I” in “team” as a means of ensuring that any skeptics in the group must fall in line. NXIVM thrived on the same peer pressures that prey on our insecurities about our bodies, our fitness, our egos; those same impulses steer our choices about politics, morality and faith.

Later episodes are striking for the level of regret that former members still struggle to express. While Oxenberg, Vicente and Edmondson are overjoyed when the New York Times finally runs a big exposé on Raniere, based on their accounts, they also have a belated reaction to the article, realizing that it didn’t convey how easy it was to fall for Raniere’s system, and how humiliated they feel to have been a part of it. Oxenberg admits she exposed her daughter early on to a number of searching, self-help experiences — ashrams, gurus, people who claimed to be selling the big answer. She was the one who took India to her first NXIVM meeting.

At one point, Vicente and Ames take a stroll on a pier and try to reconcile their roles in the harm NXIVM caused others, particularly their wives. “We didn’t join a cult,” Vicente says. “Nobody joins a cult. They join a good thing, and then realize they were [expletive]. . . . I’m hurting so bad. I wanted to be a good guy.”

“The arrogance, the pride, the sanctimonious nature,” Ames says. “I trained people to Heil Hitler. How do you un-ring that bell in your head?”

What they are grieving, really, is a failure to see the obvious and not-so-obvious warning signs. Those red flags. That little voice inside. The BS detector. Without projecting too much, “The Vow” reminds us that such failures are common — and contagious. It easily translates to the current national mood, where no one is to be trusted and nothing can be fully believed.

The Vow (one hour) series finale airs Sunday at 10 p.m. at HBO. Episodes are available for streaming at HBO Max.