(USA) Action/Thriller. Directed by Tony Gilroy. Starring Jeremy Renner, Rachel Weisz, Edward Norton, Oscar Isaac, Zeljko Ivanek. Category IIB. 135 minutes. Opened Aug 9.

There’s a downside to being a valuable commodity: people just won’t leave you alone. Ask the “Bourne” franchise and it’ll tell you all about it. Back in 2007, when “The Bourne Ultimatum” wrapped up the trilogy on a high note, Universal Studios almost immediately decided that the ultra-lucrative espionage thriller must drag on—with or without Jason Bourne. Facing the firm departures of resident director Paul Greengrass and frontman Matt Damon (who went off together to continue their man-love in the unimpressive “Green Zone”), the planned fourth installment struggled through a couple of rejected screenplays until trilogy screenwriter Tony Gilroy took up the helm. Finally, two years later than the original release date and sans its titular hero, “The Bourne Legacy” arrives, begging the burning question—why the hell should we care?

There aren’t many reasons, except maybe the charismatic new lead, Jeremy Renner. After proving his solid acting chops in “The Hurt Locker” and “The Town,” the 41-year-old Oscar nominee got ass-kicking parts in “Mission Impossible 4” and “The Avengers,” and is trodding further down the action-hero path here with the role of Aaron Cross, an elite spy who finds himself in deep trouble. Co-writing and directing an original story that parallels Robert Ludlum’s bestsellers, Gilroy—who made a formidable directorial debut with “Michael Clayton”—introduces a bigger conspiracy, in which the US Department of Defense runs a top-secret program code-named Outcome. Similar to CIA’s Treadstone, which produced Jason Bourne, Outcome has its own super soldiers; but unlike Bourne, Outcome operatives have to regularly take “chems” that enhance their intelligence, physical abilities and pain endurance. When the unseen Bourne reportedly returns to the States, threatening to expose the existence of the project to the public, boss-man Col. Eric Byer (Edward Norton) steps in to cover things up by shutting down the whole program and killing all its spies—but there’s always one that gets away.

To maintain his enhanced state (in order to save his own ass), Cross is in desperate need of chem supplies, which links his fate to that of government research scientist Dr. Marta Shearing (the ever-reliable Rachel Weisz), the sole survivor of a suspicious recent lab massacre committed by a normal-dude-gone-batshit co-worker (Zeljko Ivanek). And boy does the junkie go to great lengths for a fix—after he rescues then semi-kidnaps Shearing, the pair lands in Manila, where the chem source is located and where the movie falls into a downward spiral.

In the previous “Bourne” films, Bourne’s amnesia effectively puts the viewers in his shoes, making them follow his steps to piece together the puzzle. In “Legacy,” Cross is also searching for an answer, but as he has a fully functioning memory and we are fed detailed information about what’s really going on (thanks to the know-it-all Norton), the story appears to be lacking a sense of mystery or urgency. And if the first half-hour of the movie had the audience busy combing through the threads and intrigued by the as-yet unclear circumstances, what goes down in Manila isn’t particularly worthy of their invested interest. Why do the hastily forged passports never get checked up on? Why is Shearing’s company ID card still valid when she’s a hunted fugitive? Why is there suddenly another assassin program, and why isn’t that being shut down, too? These are just a few things that the plot doesn’t bother to explain. Soon enough, the climax takes place with an overlong motorbike chase, and things start to drag a little.

Don’t get me wrong—all things considered, “Legacy” is a pretty watchable action movie. The cast is so strong that Donna Murphy and Corey Stoll each have two lines; they even bothered to get two-time BAFTA winner Paddy Considine to play a journalist who’s shot dead in the prologue before even saying a word. The score by James Newton Howard is fittingly neat and intense, and Robert Elswit’s (“There Will Be Blood”) widescreen cinematography, though too chaotic and in-your-face for the last 40 minutes, does have a handful of glorious moments. However, bearing the “Bourne” tag means “Legacy” has to answer to a higher standard, and it simply fades in comparison to the trilogy. Not that the studio cares—should the film do well in box office, it’ll surely become the launcher of a new trilogy. “The Bourne Redundancy,” anyone?