Doug Liman started his career directing cool indie-spirited flicks like Swingers and Go. But while he may have birthed the Bourne franchise on the big screen with The Bourne Identity, his recent films like Mr. & Mrs. Smith and Jumper suggest he's lost some of the rebellion and commitment that ignited his earlier work.

With Fair Game Liman tackles a story he's clearly much more engaged with, but it's still a surprise to see his name in the Cannes program against the likes of Woody Allen, Ken Loach and Abbas Kiarostami. But in this film's selection is suggested a smart return to form. A film less mired by studio notes and high-concept effects. What Fair Game delivers doesn't quite live up to that promise, but it does introduce a director ready to move into his own, and above-the-title. It's mature, smart and engaging and, critically, strikes a new tone for Liman's work, suggesting he's got plenty of versatility.

Based on the true story of Valerie Plame, it's the tale of an undercover CIA operative (Plame, played by Naomi Watts) whose cover is blown by a government source in a national newspaper. It's a reaction to her husband's (Wilson, played by Sean Penn) claim in an article that George W. Bush's reference to weapons of mass destruction in Africa in his 2003 State of the Union address was false, because Wilson was the one responsible for the fact-finding mission which turned up no such evidence.

Adapted for the big screen, Fair Game is a political thriller akin to State of Play or Spy Game, but that it's drawn straight from life makes it all the more compelling. For Liman, this is a more serious piece of cinema than he's delivered to date, but his action chops mean it's a film which maintains its tension from scene one, even if there are no big action moments to fall back on.

But like fellow Bourne-movie alum Paul Greengrass, who just tackled topic of WMDs from another vantage point in Green Zone, the politics do tend to distract from the entertainment, and while there's a valid story to be told and message to be shared, it's neither an unfamiliar story nor a new message as it's been fed to us through news channels since it broke. That makes the whole exercise rather unnecessary – anyone interested enough to care would probably know where this was going from the off.

It doesn't help to cast Sean Penn as one of the film's leads. He's always been a fine actor, but with subject matter like this his personal politics can't help but get in the way. His performance is sound, if a little grandstanding, but because he brings such baggage to the screen it's tough to see him as the character and thus any attempts at emotion tend to ring false.

Watts, on the other hand, is on brilliant form as Valerie Plame. Aside from the fact both women look alike, Watts sells the weight of responsibility that must have been on Plame's shoulders with such confidence and impressive restraint, that she's able to keep us involved throughout.

Liman still has a way to go before he can truly be considered in the same breath as some of Cannes's stalwart directors, and should the lure of the big-budget action movie call again there's every chance we won't see another film this mature from him. But while Fair Game may not be a perfect film, if it's a statement of intent then there could be plenty of exciting things in his future.