The impulse to write what you know can be as emboldening as it can be restricting. In director Mikko Mäkelä’s soulful and observant feature “Sebastian,” a young writer grappling with this familiar conundrum begins creating a life for himself designed exclusively to be plundered for his fictional aspirations. In the process he’s forced to reckon with the porous lines he’s drawn between fact and fiction; between who he is and who he’s written himself into becoming.

Born in Edinburgh and making a living in London as a freelance writer, Max (a magnetic Ruaridh Mollica) is aching for more. He’s sick of submitting short stories he’s not too proud of, sick of composing reviews of other people’s work. Like many an ambitious 20-something before him, he feels he’s not doing enough, let alone fast enough. Bret Easton Ellis, whom he’s researching ahead of an interview, published his first novel when he was 21. As a ploy to infuse his writing with a sense of kindled urgency, Max has begun moonlighting as an escort for older men. After every encounter he orchestrates as shy, wily “Sebastian,” he dutifully sits down at his desk to add yet another chapter to his work-in-progress novel: a story about an unabashedly confident sex worker called Sebastian.

The nested-doll structure of Mäkelä’s film speaks to the writer-director’s fascination with the pleasures and perils of autofiction. Max tells himself he’s only partaking in sex work in order to flesh out the ideas he has for his novel. Yet he often feels out of sorts during those moments of sexual intimacy. Shot in tight, tangled closeups and medium shots where hungered flesh and lustful moans overwhelm character and viewer alike, those sex scenes prove to be quite moving, in turn.

Max’s performance on the page, as well as in the sheets, proves endlessly seductive: “You’ve got that wholesome boy-next-door thing going on,” a fellow escort coyly tells him, a flirtation that doubles as a cutting read that garners a sly grin out of him. “But it’s all filth underneath.” And so, as he delves into increasingly thornier scenarios (group chemsex with strangers; repeat meetings with a man who recognizes him at a literary event; a trip abroad paid by a regular customer), Max starts losing track of what he’s getting out of these encounters. He’s growing bolder but also quite boxed in by this secret life he’s come to nurture.

Eventually, those late-night meetings with men who treat him with welcome and rather unexpected tenderness unearth latent feelings Max doesn’t know what to do with. Whatever self-discovery happens, he pours back into his own work. Soon enough, he’s getting plaudits from his editor. He’s lauded for his unvarnished (and marketable) look at gay sex work, devoid of shame and trauma.

In Mollica’s hands, Max is a tightly wound young man who seeks in other people’s eyes a vision of who he is. He’s onscreen (often alone) for much of the film. His constant furtive glances keep us questioning who this lithe young lad really is, to others and especially to himself. Is he a wayward bloke who blows off bar hook-ups for client appointments that will serve as better writing fodder? A driven writer who spends late nights at his keyboard pretending to know those he sleeps with better than they know themselves? An insecure young kid who seeks approval from tricks and peers alike?

“I carve out my existence in the world using words,” Max tells an interviewer when discussing his writing. “They are the footsteps I leave in my wake.” It’s the kind of line he immediately regrets uttering, thinking it too self-serious. But crippling self-seriousness is all young writers like Max have. When his novel, like his meetings with one particular client (played with gentle beauty by Jonathan Hyde), becomes slightly more romantic, his editor insists he return to the unsparing tone he’d so perfectly honed before.

Striking a fine balance between lurid voyeurism and grounded naturalism, Mäkelä’s film is a gripping wonder, perhaps a tad too literate, with its nods not only to Ellis but to authors like Jean Genet and Cyril Collard. But with its keen, sensual eye, “Sebastian” makes its portrait of an artist as a young sex worker brim with pained authenticity about how fleeting and seemingly transactional intimacies remain rife sites of exploration for queer writers.