For a while it’s hard to work out what’s the bigger “what-if” driving Salt: what if Jason Bourne was a woman, or what if Angelina Jolie was a blonde?

About a third of the way through the film’s fairly breathless story Jolie – playing CIA operative Evelyn Salt, on the run after a Russian defector walked into her office and casually told everyone that she was a secret Soviet-era double agent – finds time to dye her hair black, which takes care of that.

But it’s a measure of how slick and effective this lightweight thriller is that from the opening scene Jolie is totally convincing as a blonde, to the point that what could have been a fatal distraction (see every other film in which she’s gone blonde, especially Life or Something Like It) quickly becomes a totally plausible part of her character. As does the somewhat slender Jolie’s ability to athletically smack down a double-figure number of highly trained US agents as she flees for reasons that remain steadfastly murky.

Is she on the run because she really is a Russian deep cover double agent activated, (with typical spy movie logic) to assassinate the Russian president on an upcoming visit to New York? Or is she running from her boss (Liev Schreiber) and CIA internal affairs agent Peabody Chiwetel Ejiofor) because the Russians have taken her husband hostage and (with typical action movie logic) she’s the only person she trusts to bring him back alive?

The story’s few twists aren’t really all that shocking, especially once you notice Salt seems to aim to wound rather than kill, but they do exactly what they need to do: provide plenty of reasons for Salt to frantically run around kicking ass Bourne-style.

Aussie director Phillip Noyce (Clear and Present Danger, Rabbit Proof Fence) does a first-rate job of combining the requirements of modern action film-making – shaky cameras and rapid cuts – with the old-fashioned need to actually know what’s going on, creating a string of chase sequences that are authentically thrilling.

Much of the fun with these films is seeing how the machine-like protagonist keeps on keeping on against the odds, and there’s a number of moments where Salt’s femininity works to her advantage (blocking a security camera with her panties, staunching a wound with a maxipad) without having to go down the sexy femme fatale path. In fact, her one big act of disguise actually makes her less of a babe.

There’s still a lot of creaky plot contrivances here – the CIA has security doors that snap shut instantly, but the White House has ones that creak closed at centimeters per minute – but this ninety-minute film moves forward so quickly there’s no time to notice them until after the end credits roll.

That those credits come after a climax that makes the whole film feel a little like a pilot for an ongoing television series is only a slight drawback: action fans should add Salt to their diet.

Salt opens in cinemas on Thursday, August 19.