You spend the first 25 minutes of The Bourne Legacy perplexed and confused. Who is Aaron Cross (Jeremy Renner) and why is he in Alaska, swimming shirtless in sub-zero temperatures, climbing mountains and fighting off wolves? What is the deal with the ex-military dude (Edward Norton) who stares grimly at computer screens, barks orders and jabs his finger in people’s faces? What is the importance of the beautiful scientist (Rachel Weisz) rocking the white lab coat in a high-tech research facility? Also, where the hell is Matt Damon?

The star of the previous three Bourne movies does not appear in this fourth (and forced) installment of the franchise. He is sorely missed. Tasked with advancing the series without its star, writer-director Tony Gilroy opts for something more ambitious than the usual reboot route. He gives us a parallel tale, taking place simultaneously during the events of The Bourne Ultimatum, in which the government decides to eradicate a group of genetically-altered super-agents used to carry out shady missions (a new, even more advanced breed is ready to replace them).

But Cross, who is one of the soldiers deemed obsolete, isn’t willing to go quietly. In his previous movies, Gilroy ( Duplicity, Michael Clayton) displayed a flair for tangled, playful narratives that rewarded close attention and doled out wonderful third-act bombs of surprise. One of the biggest disappointments in The Bourne Legacy is that there is so little to the movie beneath its surface. Once the narrative groundwork is laid down, the picture repeats the familiar Bourne formula of shady government types using technology to chase down a rogue agent. Occasionally, they send a hired gun.

Renner is solid and dependable in supporting roles ( The Avengers, Mission Impossible: Ghost Protocol), but he’s not leading-man material: He doesn’t have the soul and charisma needed to carry a giant movie like this one, and he gets drowned out by the noise. By comparison, Weisz’s panicked scientist, who doesn’t understand why her co-workers are suddenly trying to kill her, is engaging and believable and does more with the damsel-in-distress part than you might have thought possible. In one of the film’s best moments, she gradually realizes the company psychiatrist who has come to her home to evaluate her mental state may have another, more sinister motive. Weisz plays the scene so well, you actually believe her character is in mortal peril, even though she hasn’t been in the movie long enough to get bumped off.

Besides, The Bourne Legacy isn’t the sort of picture that takes risks, other than to see just how loud James Newton Howard’s score can go without causing permanent deafness in the audience. There is one fabulous set piece in the movie, a methodical mass-murder/suicide that is shot and edited with harrowing, horrifying expertise. As skilled a writer as he is, Gilroy is also a gifted filmmaker. The last half-hour of the film is one enormous action sequence in Manila — a chase by foot, car and motorcycle — that must have been exceptionally difficult to shoot and even harder to edit together. It looks fantastic, but it’s also hard to sit through, because by that point The Bourne Legacy has repeatedly proven there are no surprises to be had here, no more fresh stories to be mined from this well. No wonder Damon bailed.