Lars Lindstrom (Ryan Gosling) lives in a small town, in the small garage next door to the house of his brother, Gus (Paul Schneider), and his pregnant wife, Karin (Emily Mortimer). Lars is a loner, an emotional introvert who refuses to integrate. The world is waiting to give him a hug, but for Lars, hugs are hell. They slice through his solitude and slash at the raw nerves of buried longings. So he orders a sex doll from the internet instead.

Meet Bianca, a busty, dark-haired beauty in shiny black boots, with a silent mouth that is always ready to serve her male master. This setup suggests that we’re all set for a journey into the dark, sicko side of male sexuality. But no, the director Craig Gillespie’s film is a soft, sweet study of a man with a mental-health problem. Lars and the Real Girl is more Frank Capra than David Lynch.

Lars treats Bianca as his sweetheart, not his guilty secret. He takes her everywhere with him and talks to her as though she is a real person. We first see them together sitting on Gus and Karin’s sofa, like one of those odd couples from a Diane Arbus photo.

Naturally, Gus and Karin are shocked. Gus wants to give his brother the tough love of truth; the maternal Karin wants to tread softly. They go to see the town doctor (Patricia Clarkson), who suggests they play along so Lars can play out his problem. “Bianca is there for a reason,” the doctor says. So, under the pretext of treating Bianca for an imaginary ailment, the doctor starts talking to Lars to find out what’s going on.

Now Gus and Karin face the problem of how to tell the town about Lars and his new friend. They needn’t have worried. Everyone is so wonderfully tolerant that Lars could be dating a baby moose and nobody would bat an eye. They all talk and behave as if Bianca is a real person, and it isn’t long before she becomes a beloved member of the community. At one point, she is even praised for providing the town with a lesson in “courage”. I fear the film is not sending up the politically correct passion for inclusiveness, but actually celebrating it.

This small-town tolerance robs the story of any realism or dramatic tension. It would be better if some malignant teenage malcontent tried to burst Lars’s fantasy bubble. Instead, it all just chugs charmingly along as we wait for Lars’s inevitable disclosure - and closure.

The film never exploits its opportunity to say something about what is going on between men and women. If Bianca is the male fantasy object, is Lars the attentive and courteous boyfriend a lot of women wish they had? This lack of comment would be fine if the film was funny. Sadly, once the initial visual comedy of incongruity - seeing Bianca at the dinner table or sitting in church - wears off, there is not much left to laugh at. Gillespie never exploits the potential for social embarrassment; we’re always smiling, never squirming.

Gosling has the perfect look to portray a man driven over the edge by loneliness. He has the saddest eyes in cinema; they twitch out little Morse-code messages of despair. As a character, however, Lars never seems any more real than Bianca; he’s too much of a misfit cliché.

The film opts for the familiar dramatic terrain of the dysfunctional family who have to face up to their dysfunctions. It has no interest in the reportedly growing number of men who are turning to dolls as companions and lovers. They are known as Idollators, and some have objected to this film because it fails to recognise that a relationship with a “synthetic partner” is of equal worth to one with an “organic partner”. Would you believe it? We have entered the age of sex-doll equality.

Introducing a sex doll into the story, then cutting out sex, seems a bit of a cop-out. It just so happens that Lars is a devout Christian who wouldn’t dream of premarital hanky-panky. I suspect the sex factor has been removed because Lars wouldn’t seem so sympathetic if he were a sleazeball instead of a fruitcake. I’m not saying that Gillespie and the screen-writer Nancy Oliver necessarily had to make a full-blown David Lynch leap into the swamp of small-town life, but Bianca is far too much of a Barbie to give this film the dark edge it needs.

12A, 106 mins

Editor's choice

• Harry Potter to overtake James Bond as biggest franchise ever
• The 50 Best Movie Villains
• The 15 golden rules of theatre etiquette