SOMETIMES semi-improvised acting will save your film, and other times it will bite it hard. The Lucky Ones has a trio of above-average actors playing Army Iraq vets sharing a ride on their way across the United States in a minivan. They meet at JFK airport, just as flights are being canceled nationwide because of a blackout. The oldest soldier, Cheever (Tim Robbins), is just out of the service after having three vertebrae crushed in an ignominious accident. He rents a car, and two fellow soldiers on a 30-day pass come along for the ride. As soon as Cheever arrives home in St. Louis, he's given his walking papers by his wife, played by the unsung Molly Hagan. (Hagan has been doing working-class Midwesterners right ever sense Jerry Springer: Ringmaster.) So Cheever heads to Salt Lake City to visit his brother, taking the two Las Vegas–bound warriors with him.Michael Peña's T.K., a Hispanic trooper, has been rendered impotent with a Jake Barnes–style wound. As a merry and half-bright private, Rachel McAdams' Colee is also literally walking wounded; she carries a slow-healing but not completely disabling wound in the thigh. T.K. wants to go to Vegas to hire some first-rate hookers he's heard about who can bring a man back to potency. The script includes a fancy magical-realist touch: the dirt-poor Colee carries in her possession a guitar that was supposedly played by Elvis himself, and she's returning it to the parents of her K.I.A. boyfriend. Remember how Woody Guthrie's guitar had a sticker reading, "This machine kills fascists"? This guitar needs a sticker saying, "This machine represents the promise of America, dimmed as it is by the events of the last seven years."

Robbins underplays nicely—the stiff spine makes him look quite military. And McAdams is lightly charming. She has a believable rural accent for the part and supposedly trained hard for the role. Yet she doesn't have the sense of someone who had been surrounded by numerous men for a couple of years, much less like a woman grieving for a dead boyfriend. There's nothing really guarded about her. (She's also supposed to be very pious, yet she also approves of T.K.'s prostitutes.)

Director Neil Burger notes, "The movie I looked at the most when writing The Lucky Ones was a great Jack Nicholson movie called The Last Detail." Trying to copy that film was Burger's best inspiration. Whenever he follows it, The Lucky Ones is safe. One appreciates Burger's class-card playing, his unforced but sharp contrasting of tin-box trailers with the minimansions seen from the road. In the film's best scenes, the trio is invited to a birthday party at the kind of Kansas City country-club dwelling that looks bigger than Versailles. On the downside, the plot includes a sudden, trumped-up need for $20,000, as well as hefty product placement for Hummers and McDonald's. Still, the looseness, Rolfe Kent's subtle score and the low-key, downbeat ending makes this a film in better shape than Stop-Loss. At its best, The Lucky Ones gets at the center of a soldier's lament. The ambiguities of civilian life leave these vets lost, compared to the harsh certainties of the military.

THE LUCKY ONES (R; 115 min.), directed by Neil Burger, written by Burger and Dirk Wittenborn, photographed by Declan Quinn and starring Tim Robbins and Rachel McAdams, opens Sept. 26 at selected theaters.

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