“Salt” has most of the ingredients for a tasty, Bourne-style espionage casserole. It just doesn’t have them in the right amounts. You need action sequences, of course, and a butt-kicking hero, and a certain degree of uncertainty about whether the good guys are all completely trustworthy. A nefarious plan to assassinate, oh, say, the president adds flavor. For a nice retro feel, it doesn’t hurt to bring back a favorite villain from yesteryear, like the Russians.

All of the above is to be found in “Salt.” What it lacks is motivation. Maybe that doesn’t seem very important, but you sure notice when it’s missing.

Our heroine, Evelyn Salt (Angelina Jolie), is a top CIA spy who’s accused of being a double agent. If this is true, it would be a fairly serious blemish on her employee evaluation. She says it isn’t true, but that’s what you’d expect a double agent to say. The film is about her efforts to prove her loyalties, protect her civilian husband (August Diehl), and prevent the real bad guys from carrying out their plot.

The problem — and I’m trying to avoid spoilers here — is that we’re never given any sign of WHY she does the things she does. In a story full of double- and triple-crossers, she seems to have been chosen to fill her particular role arbitrarily. The purpose she serves in the story could just as easily have been served by one of several other characters.

If your main character changes sides, from good to bad or bad to good, we need to know why and when. What sparks the decision? This movie, directed by Phillip Noyce (“Clear and Present Danger”) from a screenplay by Kurt Wimmer (“Law Abiding Citizen”), is so intent on keeping us guessing about what Salt is up to that it omits the decision-making altogether. We don’t know what choices she has made until after she carries them out, and we never know why.

It’s a shame we don’t care about any of these people, because parts of the film are robustly entertaining. Evelyn Salt is one of those super-spies who can escape from anything, make a bomb out of nothing, and never be killed by anyone. Her ingenuity and resourcefulness often make for breezy summertime viewing. The villains’ master plan, when it’s all unraveled, is delightfully complicated and nonsensical; they seem to have counted on a few things happening that did happen but that there’s no way they could have known would happen. And while the film is never quite intentionally campy, it does make me smile to see so many Cold War-era tropes — Russians! Sabotage! Nuclear launch codes! — deployed in a film set in 2011.

Also of note are Liev Schreiber as the gruff CIA agent who insists Salt is loyal and Chiwetel Ejiofor as the counter-intelligence official whose duty it is to investigate the claims against her. Schreiber, Ejiofor, and Jolie are all well-suited to the very serious business of being spies and counter-spies. But as we’ve learned from all the really good spy movies of recent years, it’s not enough to fill the screen with intrigue and car chases. We need to feel a connection to the hero. We need a reason to root for him or her, and “that’s whose name is in the title” doesn’t cut it.

[Originally published at Cinematical.]

C+ (1 hr., 40 min.; PG-13, moderate profanity, moderate violence.)