In Arthur Newman, which opened Friday in area theaters, Blunt is Michaela "Mike" Fitzgerald, a kleptomaniac who is first found blotto on cough syrup and in dire need of a visit to the ER. Firth's Arthur Newman (not to be confused with the opera baritone famous in the mid-20th century) takes her to the hospital, and so the relationship - and the road movie - is off.
Although it's been directed by a newbie, Dante Ariola, the script for Arthur Newman is of vintage origin. Becky Johnston, the Oscar-nomi nated screenwriter of The Prince of Tides, wrote the screenplay several decades back, with Nick Nolte in mind in the title role.
That never happened. Instead, Firth, winner of an Academy Award for The King's Speech, assumes the demeanor of a gloomy Gus, and the accent of a gloomy American. Blunt, too, plays a Yank, from North Carolina.
But as the two drive around, heading for Terre Haute, Ind., they spot various couples along the way - hipsters, farmers, suburbanites - and then sneak into their homes and jump into their beds. It's a game of risky role-playing, taking on the personas, and the sexual peccadilloes, of the strangers they've singled out.
"The theory of the film is that the more we mask ourselves, maybe the freer we can be," Blunt says. "So it was lovely to explore that . . .. And to be fair, it wasn't like we were playing actors taking on these different roles. We were playing real people who were just mimicking, rather badly, people that they saw on the street, or had an affection for, or had a connection with.
"The real challenge, I found, was playing Mike in herself. When she wasn't role-playing, when she wasn't having a great time breaking into people's houses and having sex. You know, trying to figure out who she really is, and why she does what she does."
Blunt, 30, is married to actor and writer John Krasinski. They live in Los Angeles. They work a lot. He: The Office, in its final season, and Promised Land (which he cowrote), Nobody Walks, Big Miracle. He's one of the key voices in Pixar's Monsters University, coming this summer.
She: Looper, The Five-Year Engagement, Your Sister's Sister, Salmon Fishing in the Yemen. And Blunt has just finished an arduous eight months on All You Need Is Kill. She's the female lead opposite some guy named Cruise. Tom Cruise.
Directed by Doug Liman ( The Bourne Identity), from the sci-fi novel by Hiroshi Sakurazaka, All You Need Is Kill is a kind of apocalyptic, battle-strewn take on Groundhog Day in which the warrior hero is caught in a time loop of combat, death, and resurrection, combat, death, and resurrection. Blunt is a highly decorated U.S. special forces soldier, experiencing the same bloody deja vu. The film should open in March.
"It took over my life, to be honest," says Blunt, who was based in her "old stomping grounds" in London during the shoot. "I had to train for about three months before we started. Very different from Arthur Newman.
"I trained in martial arts and fighting and just any form of athleticism that I needed to work on, which was" - and here she pauses for comedic effect - "rather a lot. It was pretty intense. I have to keep up with Tom Cruise, for God's sake."
Blunt says the megastar, with whom she had crossed paths once or twice through friends, was relentlessly upbeat through the production.
"He's the biggest pro, and he's endlessly supportive, and we had a laugh, we really did," she says. "We laughed our way through the pain, as it were. We had to wear these enormous armored suits that weighed a great deal . . .. But he's just a machine. I've never met anyone quite like him. He infused the entire set with energy. He sort of infects people in that way."
And Blunt? Well, Blunt felt buff. Very buff.
"I did kind of feel like a superwoman," she says. "I felt intimidating. John, my husband, would say that he was terrified that he was going to wake up one morning and I would be benching him."
Contact Steven Rea at 215-854-5629, email@example.com, or follow on Twitter @Steven_Rea. Read his blog, "On Movies Online," at www.philly.com/onmovies.