The fourth film in the Bourne franchise, "The Bourne Legacy," may seem heady and intentionally disorienting and hard to follow at first — until you realize it’s really about drug addiction, and the lengths to which a junkie will go to get his fix.

Structurally, yes, it’s loaded with all the lies, schemes and high-tech trickery that are staples of the espionage genre. But a deeper, more individualistic source of tension propels the film along. Think of it as "Drugstore Cowboy" with an international scope and more explosions. That may help as you compare it with the first three films in the series that starred Matt Damon as Jason Bourne, the amnesiac CIA assassin of Robert Ludlum’s novels, and established Damon as the rare action star who can actually act.

‘THE BOURNE LEGACY’ Rated: PG-13 Opens today

Comparison is inevitable, especially given that a new leading man, Jeremy Renner, now plays the highly trained badass at the center of the film’s intrigue. And as a straight-up action flick, "The Bourne Legacy" does come up a bit short, except for one dizzying motorcycle chase through the streets of Manila. But it feels like Tony Gilroy is trying to do something different here, something more cerebral and potentially less crowd-pleasing.

Gilroy, who wrote or co-wrote the previous three films ("The Bourne Identity," "The Bourne Supremacy" and "The Bourne Ultimatum"), takes over directing duties as well this time, and it seems as if he’s more interested in offering a character drama about desperation than a high-octane summer blockbuster. Not that "The Bourne Legacy" is free of thrills, it’s just more grounded than spectacular. He lets the shootouts and chases play out in a more fluid fashion than the frenzied, kinetic style that’s the signature of Paul Greengrass, who directed parts two and three.

Renner stars as Aaron Cross, who’s alone in the wilds of Alaska on a training exercise at the film’s start. But he finds he’s the target of a legitimate threat when the supersecret government spy program he’s a part of hastily gets shut down with the exposure of Jason Bourne. Turns out, Bourne was not the only person given a whole new identity — he was one of many, and the new models are even bigger-better-faster-stronger thanks to a combination of little blue and green pills.

His handlers, including Edward Norton, Stacy Keach and Donna Murphy, may have done too good a job. Cross is hard to kill, and Gilroy cuts back and forth between the spy’s resourceful, globe-trotting efforts to stay alive and the shadowy surveillance rooms full of glowing monitors that illuminate his hunters’ growing frustration.

Cross finds one ally, though. Rachel Weisz plays Dr. Marta Shearing, a research scientist at a pharmaceutical giant who becomes his reluctant partner on the run. She also finds herself a target when she becomes the lone survivor of a massive workplace shooting at her lab. (The deliberate carnage would have been unsettling anyway, but it seems especially so now.)

He needs to get his hands on more of the drugs she helped concoct or he’ll revert to his former, normal self. She knows where to find them, but it’s a long and messy slog. Weisz is literally and figuratively along for the ride, called upon as she is to do little more than rattle off a lot of scientific jargon and persevere.

That means it’s up to Renner to inject the film with some personality, to find a balance between being engaging and deadly. And he succeeds in the first part of the film, showing some of the flashes of exciting unpredictability he made his name on in "The Hurt Locker" and "The Town." Going through withdrawal does his character no favors, and strands him in straightforward survival mode.

But it’s clear from the final shot (which is part of a rather abrupt ending) that more adventures with Aaron Cross are in store.