Journalist David Farrier, left, goes behind the scenes of a tickling website with its owner Richard Ivey, center, and a video participant in the documentary, “Tickled.” (Magnolia Pictures)

A crafty, unsettling bait-and-switch of a movie, the documentary “Tickled” sends viewers down a disquieting rabbit hole, into corners of the Internet, economic desperation and the human psyche that grow darker with every turn and twist.

And the twists are myriad in a tale that, with its whimsical title and amusing first act, promises to be a harmless portrait of garden-variety weirdness. Several years ago, New Zealand television reporter David Farrier happened upon a video of young men engaging in “competitive endurance tickling,” a bizarre, sexually charged sport that seemed right up his alley as a journalist specializing in human interest and pop culture.

When Farrier began to pursue the story, however, he received immediate pushback from the purveyor of the videos, a mysterious figure named Jane O’Brien who, through her legal and business representatives, hurled increasingly vile threats and insinuations his way to put him off the case. Undeterred, Farrier and his friend and co-director Dylan Reeve pushed even harder, plunging themselves into an unsavory world populated by shadowy characters and, finally, an enigmatic figure whose strange taste in entertainment led to the exploitation of and outright predation upon vulnerable, financially deprived young men.

Filmed as an investigative mystery story, “Tickled” often resembles the first-person explorations of British documentary filmmaker Nick Broomfield, inducing similar feelings of squeamishness. The story is so nasty, so depraved and troubling, that viewers may well wonder at its value beyond prurient interest. In their crusade to corner the elusive malefactor at the story’s center, Farrier and Reeve strike a blow against the abuse of power, especially in the Internet age of anonymity and credulity. Their journey to the depths can’t help but leave audiences feeling skeevy and profoundly creeped out. Like the activity of its title, “Tickled” is funny until it most decidedly isn’t.

R. At Landmark’s Atlantic Plumbing Cinema. Contains crude language. 92 minutes.