rated PG-13

As sequel ideas go, “The Bourne Legacy” falls firmly into the “Heck, why not?” category. With three strong Bourne movies already behind us, we didn’t really need another, but then again, the predecessors weren’t so deep or complicated as to be difficult to reproduce, so why not go ahead and make another? Keep the action frenetic and the spycraft engaging, and it’s bound to be fun.

“The Bourne Legacy” picks up in the background of the other movies. As Jason Bourne is tearing down the government divisions that ran “Treadstone,” Eric Byer (Edward Norton) acts quickly to destroy all evidence of related superspy-training programs, which is to say, he orders everyone involved to be killed, even the agents created by the programs.

Aaron Cross (Jeremy Renner) is one such agent, sent to Alaska as punishment for some unspecified bad behavior involving a grid. After he manages to evade the drone strike sent against him using an elaborate ruse involving wolf wrestling, he makes a beeline back to the lower 48 on an epic journey to find more drugs.

Wait… really? In fact, yes. Agents in his program are given one pill to make them physically superior, and one to enhance their mental abilities, and all the remaining action in the film hinges on Cross’s efforts to ensure he does not lose those enhancements and end up a normal person like us.

While understandable, this is not a very compelling motive. He’s not missing his identity, or confused about who he is, or trying to figure out if he’s a good guy or a bad guy, or find who did this to him—all those elements from the earlier movies are gone. Cross knows exactly who he is and how he got there, he just wants his pills. Since most of us in the audience are ourselves normal people, the horror of dropping a few IQ points and ending up like us is maybe not the most sympathetic motivation.

It’s unfortunate, because Renner has the makings of a fine Bourne-style spy, and may be more inherently charismatic than Matt Damon. But he’s given very little to work with.

The action is also much thinner and less convincing than any of the previous movies. Tony Gilroy worked on the screenplays of previous Bourne films, but this is his first time directing one of them. The action sequences lack both imagination and a sense of place, with such an unfortunate reliance on close-ups that we forget where we are. During a furious motorcycle chase, one gets the sense that it was just a mash-up of shots of traffic and shots of a motorcycle, and it doesn’t feel like any real stunts were actually executed. If you can’t do the chase scenes right, you really should not be making one of these movies.

There is also a sense that this style of spy movie is becoming dated. One of the challenges that the original Bourne movies handled well was to update the original 1980 story elements into a modern setting, but now it’s starting to seem that the world is just changing too fast to believe in traditional spycraft. Wouldn’t these spies have to be retrained every six weeks just to keep up with changing technology? If you actually sent someone into deep cover in the field for a couple of years, by the time you called on them their super-training would have missed things like, say, the iPhone and Twitter.

This is a problem faced by screenwriters, too, relying on ancient, outdated clichés to tell modern stories. Norton’s character executes almost all of his lines from an over-the-top command and control room with a Big Board straight out of “Doctor Strangelove,” and in watching those scenes we realize how far we haven’t come.