I’ve attended the Sundance Film Festival for about a decade and, until now, there’s always been a constant. After a big premiere, the men’s room adjacent to the enormous Eccles Theater is brimming with chatter. As the credits rolled on Jennifer Fox’s The Tale there was stony silence. I’ve never seen anything like it - the hushed lavatory or, quite frankly, this film.

The Tale rattled me in ways I didn’t know I still could be rattled. This deliberately paced, remarkable exploration about sexual abuse, consent and way we second-guess ourselves is the mother of all #MeToo movies. Perhaps if I knew going in that I would see (simulated) child molestation and hear the phrases predators use to lure children into thinking that their bond is “too pure for regular society to understand”, I would not have had such a visceral reaction. Would Jennifer Fox and company take it as a compliment if I told them that their movie almost made me throw up? Because it did, but only because this remarkable achievement is so damn effective.

Fox has been making documentaries for 30 years, but this is her first scripted film. It is, however, an autobiography, or at least based on a kind of dialogue between the adult Fox (as played by Laura Dern) and the 13 year-old version of herself. As a child she wrote a short story (upon which this film is technically “based”), and at the time she claimed it was fiction. Encountering that story again “now” begins a long, serpentine road to a shocking realization: Fox was sexually molested as a pre-pubescent, even though she’s held those memories as part of her self-described bloom into a maturity.

In the 35 intervening years Fox (and at this point it is hard to know if we’re talking about the actual Jennifer Fox or the version Dern plays) buried herself in her work, often on the subject of sexual abuse and female empowerment. She’s first nudged to reflection when Fox’s mother (Ellen Burstyn) finds the old story from her eighth grade creative writing class.

In it, she describes her two mentors: “Mrs. G” (Elizabeth Debicki), a strict, married trainer from a horse camp, and her lover Bill (Jason Ritter), a running coach. Fox was an introspective child in a busy home with numerous siblings, so began spending weekends on the ranch. “Mrs. G.” and Bill bond with the younger version of Jennifer (Isabelle Nélisse), but soon red flags appear.

There are many overlapping threads and timelines. Common has a small but essential role as Jennifer’s current and very supportive boyfriend, to whom Jennifer argues that she is not now nor has she ever been a victim. This is where The Tale treads into some daring and unusual waters. It’s not as if the movie states that a 13 year-old girl has the capacity to engage in a mature, intimate relationship with a nearly 40 year-old man. But it does offer the basis for that argument to be made – even if it is something of a head-fake. One of of Fox’s many skilled stylistic moves is when we first “see” the 13 year-old Jennifer. Jennifer “remembers” her as much more physically developed (and played by a more mature actress). Only when she’s shown an actual photograph does the film shift gears and introduce Jennifer as the kid she truly was.

The Tale is a difficult film. I’ll confess I wasn’t all that with it during much of the first half. I thought it meandered, over-explained things and I found the relationship between Dern and Burstyn a bit phony. This was, I now realize, setting the stage for the fireworks of the second half. Then there’s also the scenes of what young Jennifer called lovemaking, but everyone else in the world will call rape.

A closing title card assures that stunt doubles were used, and while there is no nudity, these scenes are extremely uncomfortable. Fox shoots Nélisse’s face in close-up during the act, and though I do believe in the power of art and storytelling if the artist has the goods, for some this will be a bridge too far.

Jason Ritter’s Bill is never crass. His character’s make-believe openness (or who knows, maybe it was real openness) is part of what makes him appealing at first to young Jennifer. Yet, I must warn that some of the dialogue he has during these sure-to-be-controversial scenes turned me ice cold. I can’t repeat the lines in this review, not because they are vulgar, but more because I can’t handle them coming out of my fingertips. Not when I associate them with the close-up reaction shots Fox uses.

I want more people to see The Tale because it’s such an innovative, honest and important film. It is a landmark, and Laura Dern is absolutely extraordinary. But I know for certain I’ll never watch it again.

• The Tale premieres on HBO in the US on 26 May with a UK date yet to be announced