British funnyman Ricky Gervais imagines a parallel world where everyone only tells the truth. Then one day a man is pushed by circumstance to tell a lie and realms of undreamed-of power and wealth open up to him.

The Invention of Lying is a one-joke idea that carries out its outlandish premise for 100 minutes. It begins to seem like an extended series of blackout sketches, maybe because Gervais is programmed that way, having had his biggest success in writing and starring in the original, British version of TV’s The Office.

There are many funny moments in his oddball romantic comedy, but many of them come at the start of The Invention of Lying when we’re startled by characters who blurt out the barest truths to each other with cool certainty –– that someone is ugly or fat or a loser. A TV pitchman tells the truth about the cola he’s selling, just sugar and brown water, urging people to buy it only because “it’s famous.” A waiter greets his customers with the announcement that, “I’m embarrassed to work here.” A retirement home has the legend, “A Sad Place for Hopeless Old People,” emblazoned across its front. A patient there admits, “Each day is worse than the last.” This stuff brings laughs, but it becomes more of the same the longer it goes on.

Gervais’ Mark Bellison, a writer for a film company that specializes in dull historical tracts, is described early in the film as “a chubby little loser.” He’s stuck writing about the Black Plague and he’s about to be fired because no one likes his scripts, which are, needless to say, depressing.

That’s fine with Mark’s co-workers, who don’t like him. “I loathed almost every minute I worked for you,” says his secretary (Tina Fey).

Worse, Mark can’t get to first base with his blind date, the radiant Anna (Jennifer Garner). Mark thinks of her as a goddess, even though Anna tells him right off that she’s not looking forward to their date and that she finds his chubby face and snub nose a turn off. She thinks Mark doesn’t hold very much genetic promise for any children they might have. She’s “out of his league,” Anna tells him and, sadly, Mark knows it.

Yet in the midst of a string of personal disasters, Mark finds the key to snatching triumph out of the jaws of defeat when he accidentally discovers that by telling a lie he can get just exactly what he needs. Because everyone in this odd world (actually Lowell, Mass.) has been programmed to say only the truth, they don’t recognize a lie. They take what Mark says at face value, no matter how outrageous –– that he invented the bicycle, that he’s black, that he’s an Eskimo.

Mark is awed by this newfound power and runs with it, seeing a chance at wealth and success beyond his wildest dreams. When he compassionately tries to ease the final moments of his dying mother (Fionnula Flanagan of Showtime’s Providence-filmed Brotherhood) by concocting a story about a bright afterlife where people live in mansions, are young again and incredibly happy, he touches a nerve. What he thinks of as an innocent lie steamrollers via word of mouth, catching the rapt attention of a worldwide audience that had never conceived of God or an afterlife. Gervais, a lifelong atheist, pokes fun at the staunch beliefs of organized religion, hammering them with a jaundiced comic delivery.

As his idea takes hold, Mark tries to appeal to the people, by inventing the “Man in the Sky” who controls everything, the good and the bad. Amusingly, Mark tries to squirm out of trying to explain to them why bad things are allowed to happen to good people.

Mark’s pronouncements catch even the attention of Anna, who warms to him. Yet she’s also swayed by the good looking, but self-infatuated Brad Kessler (Rob Lowe), Mark’s rival at the office and now in romance. Brad may be a snake, but Anna thinks he has good genes.

The idea for The Invention of Lying is original and some of the writing is sharp and pointed, though the script eventually seems a wee bit precious. Gervais has written himself (with Matthew Robinson) a sympathetic character that fits his personality perfectly. But good will can only go so far and long before The Invention of Lying has run its course, one can figure out just where it’s headed. And that’s no lie.

***The Invention of Lying

Starring: Ricky Gervais, Jennifer Garner, Jonah Hill, Louis C.K., Rob Lowe, Tina Fey.

Rated: PG-13, contains adult themes.

mjanuson@projo.com