''M:I-2'''s screenplay was a last-minute work in progress

No spy worth his weight in bullets would begin a mission without a thorough briefing. But ”Mission: Impossible 2,” the $90 million spy thriller starring Tom Cruise, started filming without a finished script. What’s more, Robert Towne (the sole writer to receive screenplay credit) says he was making changes to his work during the editing process as recently as two weeks ago.

Though the movie’s plot isn’t nearly as convoluted as the first ”Mission: Impossible,” the sequel still boasts elaborate action scenes, fiery explosions, backstabbing double agents, and — something new — loads of mushy stuff. This time around, Cruise’s wily hero, Ethan Hunt, makes time to fall in love. Says leading lady Thandie Newton (”Beloved”): ”What excited me was [that] this movie was going to be about a love triangle, so there was a theme that would really affect people. The film is driven by real, human, emotional significance.”

And lots and lots of car chases. In fact, director John Woo and Cruise, who doubled as the film’s producer, soon discovered that adding a dash of romance to a streamlined shoot ’em up was harder than they’d hoped. Screenwriting heavyweights Michael Tolkin (”The Player”), William Goldman (”Butch Cassidy and the Sundance Kid”), and Wesley Strick (”Cape Fear”) wrote and rewrote the script before the assignment was passed to ”Chinatown” scribe and ”Mission: Impossible” cowriter Towne.

Yet Towne wasn’t able to start with a clean slate. Because action sequences require more planning than do simple dialogue scenes, time-crunched producers had already started work on the best showstoppers from previous drafts. So Towne had to come up with a plot that tied together all the pre-existing car chases, kung-fu, and rock climbing high jinks — and still made sense. ”It was, ‘Hey, Robert, here are the action sequences, how’d you like to write us a story?”’ the Oscar winner says. ”I had never even tried to write something that way before, and it was frightening.”

Scared or not, Towne was under the gun: The start date to begin shooting in Australia was looming, and ”M:I-2” had already been delayed by Cruise’s two-year commitment to ”Eyes Wide Shut.” ”We had the script in shape about five days before shooting began,” says Towne. ”It was not an easy thing to do. The first couple of stabs at it were extremely rocky.” Though Towne says he had worked out most of the story line kinks by his third draft, the fixes didn’t stop there. Once filming was underway, Towne was flown in to continue reworking the script — a process that resumed when the film was in the editing room, and continued as late as two weeks ago.

But the writer disputes rumors that his nonstop revisions were a desperate attempt to save a faltering movie. After all, it took screenwriters Steve Zaillian (”Schindler’s List”), David Koepp (”Jurassic Park”), and Towne a total of two years to write the first ”Mission: Impossible.” And Towne isn’t convinced that the first film was the mess critics said it was (EW dismissed the movie as a ”quizzical, impersonal toy”). ”I think part of the problem with the film was the sound mix,” he says. ”Critical lines that revealed plot were very often subsumed in music cues and background noise.” Hey, when in doubt, blame the sound guy.