With his first two films ­ the much-acclaimed yet controversial In The Company Of Men and Your Friends And Neighbors ­ Neil LaBute established a niche for himself as one of cinema's most caustic commentators on the human condition. His films so far, and his plays, are characterised by unsparing dialogue and a brutal worldview in which men and women behave savagely towards each other.

No-one gets off the hook and, to keep our focus on his theme, LaBute deliberately rejects the trappings of film as entertainment: his casts are tiny and relatively low-key, his locations are deliberately anonymous, he uses few exterior shots and there is little in the way of conventional movie action. But with his third film, Nurse Betty, LaBute is attempting something altogether different: a dark comedy with hitmen, drug deals and characters hitting the road.

The biggest surprise is that LaBute ­ who initially made his name as a playwright, and whose strong suit is dialogue and monologues ­ did not write the script. Instead, he worked from a screenplay written by the comparatively little known John Richards, in conjunction with sometime producer James Flamberg. Say Labute: "Two things struck me immediately upon reading Nurse Betty: one, this script is incredibly fun and clever, and two, no-one will ever expect me to irect it. So I instantly jumped at the chance." The second surprise is, that after dealing with so many urban sophisticates and their hypocritical impulses, LaBute has chosen to start his story in a Midwestern locale somewhere in Kansas. The events are set in motion by a car salesman, Del (Aaron Eckhart, who starred in both of LaBute's other films), who is married to a soap opera-addicted waitress named Betty (Renee Zellweger).

Del is trying to find a buyer for a consignment of stolen drugs but, before he can offload them, he is murdered by a father-and-son team of hitmen ­ Charlie (Morgan Freeman) and Wesley (Chris Rock), who are working for the person the drugs were stolen from.

In spite of the subject matter, Zellweger insists that Nurse Betty is "such a sweet story." Neil LaBute won't go as far as that, but does concede that the tone is significantly different from his earlier films. "This has a much keener balance of light and dark," he admits, and the key person charged with helping him to create this delicate balance is director of photography Jean Yves Escoffier. With a broad resumé including Les Amants Du Pont-Neuf, Good Will Hunting, Gummo and The Cradle Will Rock, Escoffier has the perfect credentials to shoot a film that is much more dynamic than LaBute's deliberately static earlier offerings.

Much of the talk about the film has focused on the casting: industry pundits take the presence of Zellweger and Freeman to mean that LaBute is working his way up to A-list talent. It's worth remembering, though, that Your Friends And Neighbors featured Ben Stiller, Jason Patric and Natassja Kinski, which means that LaBute is clearly no novice at dealing with stars.

And, looking at the roles he's assigned, his thinking is clearly traditional: Zellweger's character is the perfect vehicle for her girl-next-door demeanour, as showcased in Jerry Maguire and Carl Franklin's family drama One True Thing. Playing opposite her in the romantic male lead in Nurse Betty is clean-cut former talk show host Greg Kinnear, whose Best Supporting Actor nomination for As Good As It Gets suggests he's capable of meeting LaBute's exacting demands.

More intriguing is LaBute's decision to cast Morgan Freeman against type. In recent years, Freeman's presence in a film has become cinematic shorthand for dignity and wisdom, but Nurse Betty gives him the chance to explore more escapist territory as a cold-blooded killer. His restrained style should provide an acute contrast to the high-decibel tendencies of his screen partner Chris Rock, the hugely successful stand-up comedian who played the 13th Apostle in Kevin Smith's Dogma, which debuted at Cannes last year.

If nothing else, Nurse Betty will go down in the history books for featuring a rare appearance by eccentric actor/director/author/songwriter Crispin Glover, whose fragile, birdlike presence was last seen in The People Vs Larry Flynt.

This all suggests a promising mix of mainstream and American arthouse elements. "Nurse Betty will surprise audiences," LaBute suggests. With such a volatile mix of ingredients, it can't fail to.

Mark Morris