Having won an impressive collection of Oscars, including Best Direction, Best Screenplay and Best Picture for their mesmerising amoral thriller No Country for Old Men, Joel and Ethan Coen return to comedy. It is a genre they are very comfortable with, having produced such classics as Raising Arizona, Fargo and O Brother, Where Art Thou?

However, this well-cast but self-indulgently scripted screwball comedy thriller does not get anywhere near their previous successes. Burn After Reading is very much a minor comic work in the Coen oeuvre, although certainly better (it would be difficult not to be) than The Ladykillers and the intolerable Coen-scripted Intolerable Cruelty.

The increasingly frenetic goings-on begin with analyst Osborne Cox (overplayed by John Malkovich) being dismissed from his job with the CIA ("Whose ass didn't I kiss?" he asks bitterly). He returns to his Washington home to drink, write his memoirs and bicker with his frosty wife Katie (Tilda Swinton), who is planning to leave Osborne for married Federal marshal Harry Pfarrer (George Clooney).

Meanwhile - and unfortunately the Coens' screenplay contains rather too many "meanwhiles" for coherent narrative flow - not-too-bright fitness-centre employee Linda Fritze (Frances McDormand) and her even less bright colleague Chad (Brad Pitt) come into possession of a computer disc containing material from Osborne's memoirs. Set on exploiting their find, they trigger off a series of comic capers which may well have amused the Coens and their cast, but will do little to please cinema-goers. The Coens appear to have been reaching for the kind of spiraling yet strangely logical Looney Tunes appeal of, particularly, Raising Arizona. If so, they fail, producing instead a series of mildly funny episodes without a strong enough narrative spine to weave the comedy and the unconvincing thriller plotline into a coherent whole.

The Coens do all they can as directors to drive the story along fast enough to coast over the frequent plot holes, but all their technical expertise and their skilled editing work are not enough in the face of their minor-league (for them) screenplay.

I couldn't help feeling at times that the shallowness of the enterprise was the result of the filmmakers taking a break from the considerable intellectual and technical labour that resulted in their previous movie, the Oscar-laden No Country for All Men.

The most entertaining comedy comes from Pitt who comes across as hilariously goofy. Sadly he has relatively little screen time, leaving the acting honours to be scooped by McDormand who delivers a splendidly off-centre comic performance. Clooney does nothing special and Malkovich does nothing special to excess. Which leaves the markedly less famous J K Simmons to deliver funniest and most memorable performance playing the poker-faced CIA operative whose job it is to explain what is going on.