Submitting to Alexander Skarsgard might sound enticing to many, but would you come back willingly if he sent you off the morning after your first night together with the terse command: “Buy yourself a butt plug. You’re too tight.”? That’s after allowing you to sleep on a rug at the foot of his bed, like a dog. Abuse, low-key cringe humor and unexpectedly sweet romance somehow co-exist in Brit writer-director Harry Lighton’s audacious first feature. Pillion is less about the shock factor of some very graphic gay kink than the nuances of love, desire and mutual needs within a sub/dom relationship.

“What am I going to do with you?” asks Skarsgard’s steely-eyed, leather-clad, indubitably dominant biker Ray, with a rare hint of a smile. “Whatever you want,” replies eagerly submissive Colin (Harry Melling), a shy young traffic warden from the outer London borough of Bromley who still lives with his salt-of-the-earth working-class folks.

The 2020 source novel by Adam Mars-Jones is titled Box Hill, a place forever associated with the picnic scene in Jane Austen’s Emma. (“Badly done, Emma. Badly done.”) You can almost spot hints of a subversive twist on the English comedy of manners in Lighton’s film, which is both unsettling and amusing as it nonjudgmentally maps the self-imposed emotional imprisonment of one partner and the liberating self-discovery of the other. It’s a story in which the ostensibly weak can make greater gains than the strong.

The word “pillion,” more commonly used in Britain than the U.S., refers to the seat occupied by the passenger riding behind the driver on a motorcycle. Also known in queer parlance as a bottom.

Ray belongs to a sub/dom gay biker club in which master and servant roles are firmly established by who drives and who rides pillion. Or in case that’s not clear enough, by who’s lined up face-down and bare-assed on picnic tables and who gets to use them as they please during a day out by the river. The aprons and plastic gingham tablecloths for easy cleaning are a nice touch. If you’ve never given much thought to the comfort factor of a Prince Albert piercing during sex, Pillion might raise some questions.

Colin hangs around at a village pub on Christmas Eve after performing in a barbershop quartet with his dad, Pete (Douglas Hodge). Ray sits at a corner table and doesn’t even look up when Colin passes around the straw boater for tips. But the biker strides up to the bar just as Colin is buying drinks and orders a few bags of chips for the crew playing darts. Without a word, Ray locks eyes with Colin and nods toward the cash he has placed on the bar, making it clear with just a commanding stare that the younger man will be paying. As a reward, Colin gets a Christmas card with a time and place to meet up the following night scribbled on it.

Pete and his wife Peggy (Lesley Sharp), who’s in the late stages of cancer treatment, are fully accepting of their son’s sexuality, so much so that they seem desperate for him to snag a boyfriend. Colin’s older brother cautions him to be careful around bikers, but his parents are just thrilled he has a date. His mother gets especially excited, insisting that he borrow his dad’s old leather jacket.

The date turns out to be an unromantic hook-up. They meet at a park corner, where Ray ties his dog to a fence and then leads Colin down an alley. For a second, you might fear that Colin is about to be assaulted, but when the taciturn biker strips down to fetish-wear — a hilarious bare-chested leather onesie — ready to be serviced, Colin looks like all his Christmases have come at once.

The sex is less than stellar, pointing to Colin’s relative inexperience, and Ray brusquely declines his suggestion of going for a drink afterwards. But Colin texts him and scores an invite to spend a night at his place across town. Colin is so hopelessly polite he lets Peggy force a box of chocolates on him to take as a gift — a funny moment with an amusing payoff a couple of scenes later.

The parents’ brief meeting when Ray — clearly allergic to small talk — comes to pick up Colin on his bike is endearingly awkward. But that’s nothing compared to three months later, when Ray finally acquiesces to a dinner, so Colin’s parents can meet him properly. Hodge and Sharp bring a light touch to their characters’ growing consternation over the way Ray speaks to their son. The closest he comes to showing affection is saying Colin has an aptitude for following instructions.

Melling gets tremendous mileage out of Colin’s nervous prattle as they arrive the first night at Ray’s and he’s instructed to cook dinner, then forced to stand since Ray’s dog occupies the spot alongside him on the couch.

The next morning, Colin looks out the window to see Ray lovingly washing his bike, a task he probably knows even then will never be assigned to him. Instead, he finds a list of household chores to be done. For his efforts, he is kitted out in ass-less wrestling gear (costume designer Grace Snell must have had a blast on this job) and gets to tussle on the floor with Ray. The biker then hands him some cash and says he’ll text him a shopping list.

Colin’s courteous response to the butt plug instruction is sublime: “Yeah, lovely. That sounds like a plan.” That typifies his response to being let into Ray’s world. While most of us would run a mile, Colin appears grateful for the attention of this god-like man, who defies the tough biker stereotype by playing piano and reading, his glasses almost turning him into a different person. A tattoo on his chest of three names — Wendy, Ellen, Rosie — suggests a straight past, perhaps with an estranged wife and daughters. But Ray gives away nothing.

Colin floats on air at work, seeming not even to hear an angry driver shouting insults at him over a parking ticket. Before long, his floppy hair has been replaced by a G.I. Jane buzz cut and he’s wearing a padlocked chain around his neck.

Lighton has stuck very loosely to Mars-Jones’ novel, moving the action from the 1970s to the present and eliminating the frame of 40-ish Colin looking back on the experience. He also tones down some of the more eyebrow-raising abuse.

The writer-director’s smartest move is never to deny Colin his dignity, even when he’s humiliated for disappointing Ray or getting vigorously plowed on a table. “Happy birthday, Colin,” whispers Ray once he’s done.

Both Melling and Skarsgard show an intimate understanding of how the power dynamic between their characters works, but what gives Pillion its kick is the friction sparked when Colin starts wanting more. Melling conveys the paradoxical elevation of Colin’s low self-esteem through the subservient relationship with an appealing pluckiness. He neither pleads nor demands, merely stating his wishes with a firmness that matches Ray’s refusals.

That assertive spark seems triggered partly by a quiet conversation with fellow sub Kevin (Scissor Sisters lead singer Jake Shears), who has his aging dom’s name, Steve, tattooed on his ass. (Other than Shears and Skarsgard, the gay bikers are played by real-life counterparts, who also served as advisors.) Kevin asks if Colin and Ray ever kiss, and when Colin says no, he responds, “I couldn’t live without the kissing.” It’s implicit that Kevin’s relationship with Steve goes back many years, making Colin aware that not every sub/dom couple is as rigid as Ray about rules.

Ray lets Colin get a little closer after he suffers a painful loss, but he also makes it clear that such access is temporary. When Colin proposes that they have one day off per week to do normal couple stuff like have breakfast together, hang out, even go motorcycling without the inflexibly codified roles, Ray simply replies “No,” with zero attempt at justification. But Colin refuses to back down, rebelling with a defiant act that breaks all their rules.

Rather than being punished, as he expects, Colin gets what he wants. This yields a gorgeous, sweepingly romantic sequence in which they go into the city and catch a movie. A lot is revealed by the double take and half-smile that soften Skarsgard’s face when Colin reaches over to help himself to the popcorn sitting in his king’s lap. Ray seems more playful and fun, dropping his cold daddy demeanor and genuinely taking pleasure in the company of someone who loves him.

Skarsgard plays the subtle shifts in Ray’s attitudes with surgical detail. The sudden look of fear in his eyes when their afternoon idyll slides into conventional romantic love packs searing poignancy, ushering in the sadness to come.

It’s what comes out of that sadness that makes Pillion so disarming, showing that even the most lacerating heartache can yield radical growth and self-knowledge, bringing with it unimagined power. That all this emerges from a movie full of penises (presumably prosthetic?), rough-and-tumble sex and dog collars is what makes it such a cheeky delight, not to mention a unique queer love story.

Lighton’s direction is straightforward but effective, keeping the camerawork clean and simple and making sparing use of melodic piano. He rightly keeps the focus on the actors, who couldn’t be better. Beloved veterans Hodge and Sharp bring a bottomless well of warmth and affection to Pete and Peggy, and casting glam/nu disco star Shears as a seasoned sub was an inspired choice.

Skarsgard’s cool magnetism is dialed up to maximum heat, making Ray simultaneously alluring and menacing, to the point where it’s easy to see why Colin would throw himself recklessly into a relationship that might profoundly damage him. Ray is stern and authoritative, but in the rare moments where he lets down that guard, we see a man who has boxed himself into a life deprived of emotion.

This is a breakthrough role for Melling, erstwhile Dudley Dursley in the Harry Potter movies. Colin is like a fledgling bird, all crazy-eyed intensity and compulsive chatter. It’s a joy to watch him come into his own, figuring out exactly what he wants and how to get it.