The first half-hour of The Invention of Lying, co-directed and co-written by Ricky Gervais and Matthew Robinson, is so sharply fresh, clever and laugh-out-loud hilarious that you can't help but wonder how they'll sustain it for another hour.

To be honest, they can't. But even when it's merely mildly amusing, this inspired parable, set in a parallel universe where only the truth is spoken, is so wittily winsome you'll readily cut Gervais and Robinson some slack if they don't quite succeed in going the distance.

Screened as a special presentation at the Toronto International Film Festival, where the tragically mismarketed Gervais vehicle Ghost Town was unveiled last year, Lying could be a hit for Warner Bros. when it opens October 2.

Before stumbling upon the power of mendacity, Gervais' Mark Bellison is your average snub-nosed fat guy who lives in a world where folks like outrageously frank first date Jennifer (a swell Jennifer Garner) are only too quick to point out those deal-breaking flaws.

That's because absolutely no one has the ability to tell a lie, little white or otherwise, including Mark's bullying secretary (Tina Fey) and even advertising executives who tell it like it is with catchphrases like: Pepsi. When They Don't Have Coke.

But when Mark is fired as a screenwriter for a historical film company -- he failed to come up with anything scintillating about the Plague -- he inadvertently comes up with his first fib and witnesses his life changing in unexpected ways.

On the surface it might sound like a more erudite Liar Liar, but Gervais and Robinson take what might have been a cute concept comedy and elevate it to delicious heights.

Things admittedly get clunky in the third act, when they attempt to work a convincing Gervais-Garner romance into the glib proceedings, but the truth is perfection's a minor quibble with the likes of Fey, Jeffrey Tambor, Rob Lowe, Jason Bateman, Jonah Hill, Philip Seymour Hoffman, Christopher Guest, Louis C.K. and Edward Norton providing expert comic backup.