Knight and Day 

There’s a running gag in the new Tom Cruise/Cameron Diaz vehicle that’s funny the first couple of times. Cruise is an über-competent superspy trying to protect Diaz, an innocent bystander. He’s so competent that, whenever our ditzy heroine starts freaking out, he simply drugs her, tosses her over his shoulder and proceeds with his exploits. We watch through Diaz’s blurring, woozy eyes as her hero, swinging upside down in some baddie’s torture chamber, assures her in his perky way, “Don’t worry, I got this!”

If you want to satirize the Bourne movies and “24,” with their impregnable secret-agent heroes, you could do worse than this joke. But Knight and Day never does any better. By the end, the slipping-a-roofie gag seems like a metaphor for the viewer’s whole experience of the movie: A lot of stuff happened, and it should have been important, but for us it’s all a blur.

Knight and Day belongs to the action-romantic-comedy subgenre, which doesn’t appear to have progressed much since the heyday of Chevy Chase and Goldie Hawn. The title reads as a gesture of desperation — yes, the hero’s last name is Knight. Most of the movie, directed by James Mangold (who made the juicier genre flick 3:10 to Yuma), is similarly uninspired.

Expect the hero and heroine to meet under unlikely circumstances and endure misadventures and misunderstandings. Expect a fist fight that takes place in Austria to involve wurst, a car chase that takes place in Spain to involve a bullfight, and an interlude in the Azores to involve Diaz in a bikini. Expect the plot to revolve around an impossible high-tech gadget that everyone in the world wants. Expect Paul Dano (as the device’s inventor) and Peter Sarsgaard (as a rival intelligence agent) to deliver paycheck performances. Just don’t expect Cruise to break a sweat.

But enough with the negativity. I’m going to give due credit and say Knight and Day is far more endurable with Cruise and Diaz than it would have been with, say, Adam Sandler and Eva Mendes (who were among the many actors actually considered). The opening scenes are even kind of fun. Diaz’s character, June Havens, allows Cruise to chat her up on a transcontinental flight, rolling her eyes at his corny Man of Mystery lines. Being single, though, she decides he’s a decent catch and plays along. Then she emerges from the restroom to find he’s killed everyone else on the plane, pilot included.

It’s a chick flick gone off the rails: Cruise’s character is a genuine Man of Mystery, but he’s also quite possibly stark raving mad. His bright-eyed unflappability does nothing to discourage this supposition, and Diaz reacts with realistic numb terror. When she stops doing that and starts saying, “He makes me feel safe” — well, that’s when the movie stops owning its twisted premise and turns back into a regular chick flick. A bad one.

The film’s real suspense involves not shootouts and MacGuffins but the stars’ faces. Let’s face it: While both actors are skilled, we’re not talking about master thespians who disappear into their roles here. Are these attractive-but-aging icons still bankable? Do they still have the comic timing to compensate for a few crows’-feet and some silly public antics? From some angles, maybe. But weekend box office is almost as cruel a test of staying power as a high-definition lens.