Movie Sneaks:  Melissa McCarthy-Rose Byrne chemistry is the secret formula in ‘Spy’

Call it an un-buddy comedy. Or maybe a tale of how enemies become frenemies. Regardless, the new film “Spy” is largely rooted in the unusual chemistry of actresses Melissa McCarthy and Rose Byrne.

In the film, McCarthy plays Susan Cooper, a CIA analyst who is typically deskbound behind a bank of computers guiding far-flung field agents through dangerous missions via radio earpiece. When her favorite colleague (Jude Law) goes missing, she finds herself sent on a European sojourn that brings her face to face with Byrne’s character of Rayna Boyanov, haughty and dangerous Oxford-educated daughter of a notorious Eastern European arms dealer. Also in the cast are Bobby Cannavale, Jason Statham, Allison Janney and Miranda Hart.

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The freewheeling espionage comedy is written and directed by Paul Feig, who also directed McCarthy in the hit comedies “Bridesmaids” and “The Heat.” (McCarthy earned an Oscar nomination for “Bridesmaids,” a rare acknowledgment for a comedic performance.) It was “Bridesmaids” that also first brought together McCarthy and Byrne, who then reprised their off-kilter chemistry while presenting at the 2012 Academy Awards.

Yet when Feig was writing “Spy” he assumed McCarthy’s busy schedule between her film career and TV’s “Mike and Molly” would make her unavailable. So he hadn’t written the story with either actress in mind.

“When I cast the two of them, I didn’t know how they would play it. So I just got them in a room and read the scenes to try all kinds of things,” Feig said. “And then when suddenly Rose slipped into this cold British accent and just started being really mean to Melissa, it was just, ‘That’s it, that’s hilarious.’ So we retrofitted the script to that.

“And on a personal level, they just really get along. Rose breaks constantly, she’s constantly laughing, and Melissa makes her laugh more than anybody. And that creates a kind of tension that just works, it adds this weird energy that you can’t describe, but it’s also where that chemistry comes from.”

The pair’s seemingly mismatched sensibilities, with McCarthy’s American can-do enthusiasm against Byrne’s more sophisticated Continental-style reserve, creates a funny pairing between Susan and Rayna. Byrne’s faux Bond villainess busts on McCarthy for her looks and behavior at every turn, even after a glamorous makeover before entering a swanky European casino. After a series of reversals, each one thinking they’ve got the jump on the other, the duo come to recognize something like respect between them.

“It’s just not a dynamic you have very often,” McCarthy said. “First she thinks she’s got me, and then I’ve duped her, and we just kept one-upping each other. I think at a certain point both characters were like, ‘What is happening, what’s going on?’ They seem extreme polar opposites, but it’s bizarre, this weird fascination Rayna has with Susan and Susan’s sort of fascination with her.”

Susan isn’t a bungler and is in fact well versed in how to be a field agent but simply doesn’t have real-world experience. Capable and competent, what she largely lacks is confidence. Inspector Clouseau she is not.

“I think there’s a big difference between bumbling and inexperience,” McCarthy said. “You’re watching her gain her footing, actually in the midst of it, which I think is very different from somebody who just doesn’t know what they’re doing.

“She knows everything, knows tactically all these things but is not used to running with a gun and being aggressive,” McCarthy said as she sat with Byrne just before the world premiere of “Spy” as part of the South By Southwest Film Festival here.

Though many think of Byrne as a dramatic actress based on her role in the TV series “Damages,” her part in “Spy” continues a run of comedic performances that really began with “Get Him to the Greek.” Though last year’s hit “Neighbors” was marketed as a battle-of-the-bros picture starring Seth Rogen and Zac Efron, audiences also responded strongly to the relationship between Rogen and Byrne. The film became an unexpected portrait of contemporary marriage as equal partnership that avoided turning Byrne’s character into the hectoring killjoy she might once have been.

In a sense, it’s a surprise that people are surprised that Byrne is funny. As Rayna, with her high-hat demeanor, sky-high hair and tacky tight clothes, Byrne goes about as broad as she has while maintaining an undercurrent of genuine emotion and pathos.

“I think people find it hard to place me,” Byrne said. “I’m Australian, people think I’m English, but I was on a TV show where I played an American and then I’m in a comedy like ‘Bridesmaids’ or ‘Neighbors.’ And with comedy I can be the straight man, which people don’t associate with being funny.”

Byrne earlier in the year finished a run on Broadway in “You Can’t Take It With You” and was recently seen in the indie comedy “Adult Beginners.” McCarthy, meanwhile, has been shooting the comedy “Michelle Darnell,” directed by her husband, Ben Falcone, from a screenplay written by the pair along with Steve Mallory.

In looking to be both a credible espionage thriller and broad character-driven comedy, “Spy” is a movie that wants to have it all.

“To me, it’s not even a spoof, it’s a spy movie that is funny,” Feig said. “To me, it’s if a real person suddenly got sent into the field and what would really happen. So that’s my hope, an audience will appreciate the tone that we hit and the tightrope that we walked. It was really tough.”

mark.olsen@latimes.com

Twitter: @IndieFocus