Imagine Before Sunrise except they’re both gay men, the chatty night unspools almost entirely inside a rented LA house, and also one of them is a convicted paedophile who has secretly lusted after the other since he was a 12-year-old kid at school. Discomfort, not romance, is on the cards in Blue Film, the smart, audacious second feature from 26-year-old director Elliot Tuttle. Boldly non-judgemental of its characters, the claustrophobic thriller knowingly presents incendiary ideas and dares viewers to sit through the mounting discomfort.

A confident camboy who usually cashes in on findom, Aaron (Kieron Moore) believes he’s struck it lucky when a stranger offers him $50,000 to spend the night with him. Arriving in the client’s living room, Aaron is confronted by a much older man in a mask – not too different from the anonymous customers who hide behind their keyboard – only to realise it’s his former English teacher, Hank Grant (Reed Birney), a man who was arrested for trying to have sex with another pupil. Over a webcam, Aaron typically indulges anyone’s fetish. Face to face with a convicted paedophile, though, the hulking twentysomething crumbles as he reconsiders the limits of his job – especially as Hank’s roleplay request is unsettlingly specific.

Three years ago, Tuttle was in LA, journalling about his memories of having a crush on a teacher. “I was watching a lot of Catherine Breillat films and thinking retroactively about my adolescent sexuality,” says Tuttle over a video call from his home in New York. “Your brain isn’t developed enough to morally qualify your attraction. But as an adult, I think: what did I actually want to happen? It then became a film about loneliness.” Tuttle also knows people who had trysts with their teachers after leaving school. “There are parallels that make the story feel less far-fetched to me.”

Over pizza and beer, Aaron and Hank reminisce about school and psychoanalyse the other as if they’re on a pseudo-date. Defiantly sex-positive, Aaron defends his job to Hank as a lucrative way to exploit his physique; the former teacher, meanwhile, attempts to explain that he was abused as a kid, which has led to his own sexual attraction to children. Further queasiness ensues when Hank claims to have always “loved” Aaron, even if he was sacked for pursuing a different 12-year-old boy at the time. Despite his personal disgust, Aaron is reluctant to leave and even allows Hank to shave off his hair, an act seemingly designed to physically de-age him.

“I knew while writing the film that there’s a danger of sympathising with a villainous figure,” says Tuttle. “It was important to do as much research as I could. I’m a gay man, but I’m also not a sex worker. And I’m not a paedophile.” He laughs at the awkwardness of stating that fact out loud. “These two characters aren’t meant to be representative of any groups, but I needed to do research to write them as honestly as I possibly could. I have to know how Hank moves through a room, and what he’d say. I hope viewers take the film in good faith. It’s certainly not intended to be an empathetic portrait of the act of paedophilia. I hope anyone going into this is on the same page that paedophilia is an immoral, criminal act, and then we can watch the film.”

Amongst the documentaries Tuttle watched, the most helpful was Pervert Park, a 2014 film about a community of sex offenders who live together in Florida. “They were released from prison and hold each other accountable,” says Tuttle. “The common thread is that many convicted sex offenders were abused as children. That’s fairly consistent across everything I watched. Many of them have a warped understanding of sex and love, and how to express it. Again, none of this is a justification for the act of paedophilia. I hope we can all go, ‘Yes, it’s wrong. Now let’s watch the movie.’ It was worth interrogating how a person might become this way, or if they were born like that. No one’s really funding research on it.”

“I knew while writing the film that there’s a danger of sympathising with a villainous figure”

The film’s ever-shifting power dynamics also acknowledge societal taboos. If Hank served prison time for his crime, to what extent should he still be punished? If Aaron is a consenting adult, then what sex acts should be off-limits? And if Aaron is the fit, muscular gym bro opposite a frail, ageing, almost unemployable loner who’s shunned by strangers, who is more likely to be in physical danger when enclosed in a locked room? The complexity of both actors’ performances keeps the drama ticking. Birney bravely conveys his character’s monstrous behaviour while presenting a sad soul doomed to solitude. In contrast, Moore reveals Aaron’s fragility beneath the bravura and tattooed abs.

Shot for only $50,000, Blue Film miraculously never feels like a play. One factor is the integration of mini DV camcorder footage shot by Hank, which Tuttle refers to as “in the Venn diagram of a snuff film and family home video – that’s what Blue Film feels like to me”. Mostly, though, it’s the expansive, explosive dialogue that, when I saw it, led to a stunned, shocked silence in the room. It was only afterwards I realised that Blue Film, a drama heavily hyped for its boundary-pushing, has a distinct lack of nudity. “I liked the idea of making a film where the ideas were the dangerous part,” he says. “Everything else felt like a hat on a hat.”

Tuttle informs me that viewers’ reactions have differed greatly. Some are deathly quiet during the film, while others are vocal and reactive. “I wanted to make a film that, by design, had a very unique relationship with each audience member,” he says. “The audience member can meet the film where they’re willing to meet it. I’m happy if the controversial parts of the film get people to see the film. I want people to say whatever they want about it.”

Blue Film is out in UK cinemas on September 11.