Tom Cruise and Cameron Diaz in an over-amped but underpowered spy tale. Tom Cruise and Cameron Diaz in “Knight and Day” Photo: Twentieth Century Fox and Regency Enterprises Anyone who’s ever been trapped on a plane flight from Hell — squashed by sprawling seatmates, battered by passing backpacks, besieged by squalling brats — will appreciate the elegant simplicity of Tom Cruise’s solution to similar problems: He kills everybody. Literally. But then they were trying to kill him. Even the pilots. Which is why they’re dead, too. Emerging from the loo, Cameron Diaz is surprised to find that she and Tom are now alone, unless you count corpses as company. And she’s worried — the plane is diving fast. Tom will handle that. (“No need to panic.”) But then what? The answer to that question has been clear in every espionage-romance dating back at least to Hitchcock’s “The 39 Steps.” The answer is: Run! If only “Knight and Day” gave these two much else to do. Playing rogue CIA agent Roy Miller, Cruise deploys his smooth charm to ravishing effect — we’re reminded again of what a supple comic actor he can be. And as innocent bystander June Havens, Diaz, with her eager eyes and engulfing grin, is adorable throughout. But the script, by first-time screenwriter Patrick O’Neill, doesn’t have enough of the breezy wit that makes a classic spy-chase movie like “North by Northwest” so pleasurable. There are some good lines. (Noting that trouble-magnet Roy has been wounded at one point, June deadpans, “You have to go to the hospital. Prison, maybe.”) But director James Mangold (“Walk the Line”) is mostly intent on goosing the action along from one nifty set of stunts to the next. The stunts are pretty great — especially a heavy-damage highway chase (which seems fresher than usual here) and a wild escape through a Spanish bull-run stampede. But we miss the stylish downtime that would allow us to catch our breath. And we miss the romance. Cruise and Diaz have real chemistry, but the script doesn’t enable them to do much with it. (Although there is a cute moment when she wakes up in a bikini she wasn’t wearing when she passed out. Too bad this sexy tease doesn’t build into anything interesting.) In the traditional way, the story is a flimsy thing; and in the traditional way, that doesn’t matter. Roy is being chased by a team of his former CIA colleagues led by an inscrutable character named Fitzgerald (Peter Sarsgaard). Fitzgerald is convinced that Roy has lost his mind and absconded with an ultra-powerful device called the Zephyr. (“The biggest thing since the sun,” Roy says.) The determined spooks chase Roy and June — who has fallen into this mess by sheerest accident — from Boston to the Azores (where Roy maintains a private island) to Austria (look out for the assassin!) to the Spanish villa where an international arms dealer named Antonio (Jordi Moll
