Independent Lens: An Honest Liar. PBS. Monday, March 28, 10 p.m.

There's something bewitchingly charming—not to mention bold as brass—about a documentary that starts off a montage of its hero introducing himself to various TV audiences as "a liar, cheat, charlatan and fake." And neither An Honest Liar (airing as an episode of the PBS documentary series Independent Lens) nor its subject, magician-turned-debunker James Randi, will let you down.

Randi, once a master mind reader and escape artist, has for the past four decades mostly concentrated on exposing charlatan psychics and faith healers, including an epic scorched-earth campaign against Israeli mentalist Uri Geller. (Randi even refused to shake Geller's hand: "Do you really suppose Churchill and Hitler would shake hands?")

In An Honest Liar (which had a brief theatrical run in 2014 but remains mostly unseen outside the festival circuit), veteran documentarians Justin Weinstein and Tyler Measom follow the 88-year-old Randi through his multiple careers, starting with his schoolboy fascination with magician The Great Blackstone, who levitated his pretty assistant. (The zenith of Blackstone's career was in the 1940s, and he died 50 years ago, but Weinstein and Measom, who've done a masterful job of assembling archival footage, actually found an old film clip of the act.) It wasn't long before the teenaged Randi ran off with a traveling carnival and started his own magic act.

Yet Randall Zwinge, as he was still billed in those days, found success, a growing disquietude came along with it. Strangers stopped him on the street asking for tips on stocks or the fidelity of their fiances, even offering him money for his psychic counsel. Randi thought he was doing parlor tricks; the realization that "people really do believe in this nonsense" stunned and then appalled him.

He began centering his act more around his uncanny talents as an escape artist. Highlight: Slipping out of a straitjacket while dangling from a chain over Niagara Falls. But when he had to be hospitalized with two fractured vertebrae after a botched version of his trademark escape from a sealed milkcan filled with water (though he briefly returned from the hospital to advise the audience that "it's not something I would recommend you undertake as a hobby"), Randi became a fulltime debunker of psychic swindlers and frauds.

An Honest Liar includes a dizzying and hilarious array of Randi's TV appearances over the years, using magician stagecraft to expose psychokinetics and psychic surgery. He even downed a week's supply of homeopathic sleeping pills without cracking a yawn. The most heroic took place on The Tonight Show, whose host Johnny Carson—an amateur magician himself—was a Randi admirer.

Carson had consulted Randi in preparation for a visit from Uri Geller, whose ability to tell which one of 10 sealed film canisters contained a steel ball-bearing had wowed the Pentagon, wracked as it was with Strangelovian fears of a growing Ball-Bearing-Film-Canister Gap with the Soviets. Randi, who noted that Geller was always presented the canisters on a tray, which he slightly turned this way and that in apparent contemplation, advised Carson to glue the cans down: Geller was watching the tray for subtle movements that gave away which canister contained the ball-bearing.

The result: 20 minutes of dead air that ended in the frustrated Geller declaring that "I don't feel strong tonight." As marvelous as that was, it probably doesn't match Randi's Tonight Show appearance in which he played secret radio transmissions to a Los Angeles faith-healer's hidden earphone that enabled him to diagnose and then "cure" illnesses. Carson's blurted on-air reaction: "Oh, shit!"

Randi didn't hustle all those years in the carnival without developing killer showmanship chops. (When I visited his home for a newspaper interview a couple of years ago, he randomly tossed off a little mind-reading trick—he somehow divined a word I picked out from the middle of a book that I chose from 4,000 or so possibilities—that left me utterly bedazzled.) And one of the things that makes An Honest Liar so entertaining is that it never loses sight of that fact. The film is full of endearingly cheesy stuff like footage from the 1950s TV show Cross-Canada Hit Parade, where the hostess sang "(You've Got) The Magic Touch" while Randi extricated himself from a straitjacket while hanging head-down over the stage.

But, fun though Randi may be, he's got a serious purpose. As a fellow magician observes in An Honest Liar, he's suggesting that life is best lived as an extension of the scientific method—that while people may not always be rational, the world is, and anything that seems to run contrary to that principal should be challenged and questioned. And the corollary is those who seek to promulgate the irrational are charlatans and mountebanks. "It's okay to fool people as long as you're doing that to teach them a lesson, which will better their knowledge of how the real world works," argues Randi.

Sadly, for all the battles Randi has won in that campaign, he may be losing the war. Uri Geller, who in a sensible world would have vanished forever after the debacle on The Tonight Show, scarcely missed a beat in his career and even now can be found on the home-shopping channels, making a small mint off selling psychic-powering crystal jewelry. "Pick up the National Enquirer or any other paper and you'll find a billion psychics," he brags in An Honest Liar. "It's much bigger than ever." And you thought the presidential election was depressing.