In journalistic circles there's a saying "hang the truth...tell the legend". Basically, it means don't let the facts get in the way of a good story.

Of course, reporters are constantly accused of making things up¿but American features writer Stephen Glass went one better - he conjured up whole feature-length articles.

What made his shady achievement all the more notable was that he was working for Washington DC's The New Republic, the eighty-year-old "in-flight magazine of Airforce One."

Writer and director Billy Ray's straightforward treatment - based on an article in Vanity Fair - is a surprisingly compulsive tale of misplaced trust that makes Walter Mitty look like the model of veracity.

On a periodical where the average age was 26, Glass comes across as very much the junior reporter courting popularity by handing out gum and Coke to his colleagues.

However, he's also regarded as the magazine's speccy wunderkind, bringing in a series of off-kilter yet socially relevant stories seemingly at will.

Hack Heaven is the latest - a cracking yarn about computer nerds naming their price to come on board major companies to shore up security they earlier breached themselves.

Glass writes it up and the story is duly despatched to the magazine's army of fact-checkers, lawyers, editors and copy editors to scrutinise for everything from a libellous comment to a misplaced comma.

Given the green-light the story appears...only for an obscure internet magazine to point out none of the people quoted in the story exist. Neither does the hacker. Or the company said to have signed him up.

It would be easy to file this oddity in the "you couldn't make it up" bracket. But, of course you can make it up - and it turns out Glass did in 27 of the 41 articles he wrote for The New Republic.

Christensen is a revelation as Glass, his richly detailed portrayal of a psychotic fantasist light years away from the lump of wood that clunked its way through Star Wars Episode II.

Excellent support in this tightly plotted tale comes from Sarsgaard as the editor who must catch the flak and there's a neat sidelong look at the office politics sparked by Glass's creative writing.

Following his dismissal, Glass followed his established career trajectory...and qualified as a lawyer.

He also wrote a novel called The Fabulist - about writer who makes stories up.