The new Ricky Gervais film, “The Invention of Lying,” postulates a world in which no one has ever told a lie. We know this because the hero, Mark Bellison, played by Gervais, tells us all about it in an opening voice-over. It is the first, small warning sign that the movie may not be firing right: what level of confidence can you have in your own comic device—the conceit that will power the whole story—if you feel the need to explain it before the drama gets under way? One delight of “The Truman Show” was the onus it placed on viewers from the start, both daring us and trusting us to work out, at our own speed, just what the hell was going on in that spotless seaside town. No such joy from Gervais, who wrote and directed the new film with Matthew Robinson, and who seems to have mislaid the T-shirt that is handed to every first-time movie director—the one that reads “Show, Don’t Tell.”

This is a shame, because the conceit itself is ripe with possibility. Entire segments of ordinary life are drained of the color and flavor that we have come to expect: advertising, for instance, is reduced from a blaze of slogans and jingles to one sallow guy on TV, holding a can and a glass and saying, “I’m asking you to not stop buying Coke.” A while later, we see a rival message on the side of a bus: “Pepsi—when they don’t have Coke.” On the basis that imagination, too, is no more than a fancy, upmarket word for fibbing, acts of fiction remain unknown; at Lecture Films, the movie studio where Mark toils—he is introduced as “one of our least successful screenwriters”—the typical product consists of a blazered bore reciting a plain historical narrative woven from verified facts. Mark is responsible for the fourteenth century, although not for much longer, since he’s about to get fired. This is cheering news to his colleagues, such as Shelley (Tina Fey), who announces brightly, “I loathed almost every minute that I worked for you,” and Brad (Rob Lowe), who says, “I’ve always hated you.”

As I listened to this volley of invective, I thought, Is Gervais cheating here? Is there not already a slight, illogical shift in his central gag? Just because humans can only tell the truth does not, surely, mean they must do so—that they are compelled to blurt it out on every occasion. After all, to suppress a malicious instinct is the task not strictly of fabrication but of good manners, and neither Gervais nor his movie is nihilistic enough to propose that goodness itself is a fraud. It is almost as if a new strain of Tourette’s syndrome were spreading through the population; when Mark goes to meet a date, Anna McDoogles (Jennifer Garner), she greets him at the door with “I was just masturbating.” It gets a laugh, but it also sets a tone of helplessness, with characters endlessly victimized by their own loose tongues. “I had a better time than I thought I would,” Anna admits as she says good night.

We have heard something similar before, in “Liar Liar” (1997), which presented Jim Carrey as a lonely blurter in a mendacious world. (“I’ve had better,” he said, when a lover, settling back after sex, asked him how it had been.) Here the situation is reversed. Everyone dwells in veracity except for Mark, who, one day, at a bank, suddenly tells a lie; we watch it happening inside his brain, a rare synaptic spark, and it nets him five hundred dollars. (I loved the notion that, like a child grappling with fresh concepts, he doesn’t have any words for what he just did: “I said something that wasn’t” is the best he can manage.) From here, the game is on; Mark can reinstate himself at Lecture Films and dream up random plots, crammed with spaceships and ninjas, and earn a fortune for his pains. No one doubts him, because, until now, there has been no room for doubt. He can say that he’s black, and the person listening will reply, “I always knew it.” He can instruct a total stranger to go to bed with him, saying that, if she doesn’t, the world will end, and she will comply. Above all, he can comfort his aged mother (Fionnula Flanagan), as she fades away in a nursing home—“A Sad Place for Hopeless Old People,” it calls itself—with an off-the-cuff account of a radiant afterlife, complete with mansions, where she will continue to exist. “Go on,” one of the nurses urges him.

So he does, and “The Invention of Lying” promptly lurches into another gear, with Mark finding fame—first local, then global—as a Moses figure, with a hint of John the Baptist. The difference is that those men believed what they foretold, whereas Mark makes it up as he goes along, scribbling nostrums on whatever comes to hand. “Everything you need to know is written on these pizza boxes,” he declares to a crowd of people gathered outside his apartment, telling them of a mysterious “man in the sky” who controls their destinies, and promising them eternal ice cream if they behave well on earth. Audiences here should be reminded, at this point, that Gervais found his fame on the BBC, with “The Office” and “Extras,” and that the execration of religious faith, specifically Christianity—plus a reflex sneer at the fools who fall for it—has, in the past decade, become the default mode of British cultural life. It makes sense, I suppose, for Gervais to use his film to air such mockery, if spiritual belief genuinely strikes him as a lie like any other; the plan would carry more weight, however, if he didn’t use the rest of the film to air his transcendent belief in Ricky Gervais.

There is a form of self-deprecation that can tighten into self-pity and, from there, mutate into a ready-wounded pride, and that, pretty much, is the tenor of this movie. “If you’re a chubby little loser, you’re all alone, at the bottom of the pile,” Mark says at the beginning, and the plaintive note is struck time and again, to the point of embarrassment; even when his lot improves, Anna still spurns him as a mate, because he would be likely to sire porky little Marks with snub noses. “Does being rich and famous change your genetic material?” she asks, and the question is one that Hollywood has put to every talented, smart, but unhandsome soul who has ever arrived at its gates. You can feel Gervais using all the means at his command (he co-produced the film as well) to agonize over the one aspect of his person—his appearance—which is not his to command, and never will be. The result is most peculiar: a vanity project made by someone who wishes he had more to be vain about. “You’re the sweetest man I’ve ever met,” Anna says, adding, “You’re my best friend.” The very phrase, as generations of men can confirm, is like a bell that tolls the death of romance. But then, without warning, “The Invention of Lying” changes gear once more, and turns into a teary rom-com; for reasons that I still can’t fathom, the beast gets his beauty after all. Did somebody fix his genes?

The movie is no easier on the eye, or the ear, than its whining hero. Even the non-office scenes have a strip-lit look—an unconscious homage, you might say, to the scene of Gervais’s first triumph—and, as for the soundtrack, it’s like being haunted by the ghost of Easy Listening Past. Supertramp and the Electric Light Orchestra are one thing, but Donovan: there’s no excuse. And what really galls is not the songs themselves but the greasy way in which they are wrapped around crucial passages of action, to muffle any awkward transitions; thus, once Mark has armed himself with white lies, he strolls off to reassure all the other miserable folk we have encountered so far—old-timers, bums on the street, a bickering couple—with a smile and a word in their ears. But what word? We can’t tell, because Elvis Costello is busy belting out “Sitting” by the artist formerly known as Cat Stevens.__

The last third of the movie is as bad as anything I’ve seen this year, with the laughs trailing off, and half of the supporting characters, the zestier ones, being airbrushed from the frame. (What director in his right mind would drop Tina Fey from the proceedings?) It’s a curious elision, because, until now, some of the best lines have belonged to passing figures; I especially liked the woman at the reception desk, in a restaurant, who welcomes the ravishing Anna with the words “Hi, I’m threatened by you.” As befits the creator of “Extras,” Gervais is keenly attuned to those on the fringes of life: to the no-hopers and their even sadder next of kin, the hopers. That is a very British predilection, and it may be one reason for his wincing unease when placed at the hub of events; as with Sacha Baron Cohen and, years ago, Peter Sellers, you get the perplexing sense of a highly gifted, essentially shy man, far from comfortable in his own skin, forcing himself into the spotlight. Toward the end, “The Invention of Lying” becomes almost a one-man show; we find ourselves in a traditional church (who built that?), with the Cross digitally removed from its steeple and an icon of Mark, with outstretched arms, above the altar. So, the sweet best friend with the snub nose not only gets the girl; he gets to play the man in the sky. Talk about invention. ♦