By Anthony Breznican
August 15, 2014 at 04:00 AM EDT

It’s early summer, Long Island. The sun is shining, the birds are singing, and Adam Driver is pacing. He lurches back and forth on the street outside the house where This Is Where I Leave You is shooting, his lanky frame stooped as he runs his hands through his nest of black hair. It’s hard to tell whether he’s trying to psych himself up or cool himself off. His costars never know either.

”Look at Driver out there. That guy is a f—ing panther,” says Jason Bateman, peering out the second-story window at the Girls star, who plays Bateman’s little brother in the emotional family comedy. ”He finishes a scene and just stalks it out.” Bateman shakes his head. ”Raw talent on that guy.”

Nearly a year later, with the film heading to screens, Driver isn’t surprised to hear he was observed stomping around between takes. ”That was the great thing about shooting in an actual house — you couldn’t escape anything,” he says. ”You turned a corner and there would be, like, Tina Fey and Jason Bateman. It was very much a family dynamic.” In other words, no privacy.

In Shawn Levy’s adaptation of the 2009 Jonathan Tropper novel, Driver plays Phillip, the youngest and most freewheeling of the four Altman kids, who reluctantly reunite for their father’s funeral at the behest of their pushy, touchy-feely mother (Jane Fonda). Phillip brings his cougarish girlfriend (Connie Britton) and reopens old wounds with his bickering siblings: the down-on-his-luck Judd (Bateman), the well-off but lonely mom of two Wendy (Fey), and the hard-bitten, dependable eldest, Paul (Corey Stoll).

Driver, 30, has roles in half a dozen films in the works, among them a major top secret part in Star Wars: Episode VII, but it’s his performance as the caring, charismatic, and sometimes scheming Phillip that may make him a movie star. On the basis of Girls, Driver already had a fan in Levy. The director even reshuffled the film’s production schedule and got the other actors to agree to shoot on weekends so Driver could work around his commitment to Lena Dunham’s HBO series. ”I knew people were going to love Driver,” Levy says. ”Who he is on Girls is amazing, but it isn’t the full portrait of him. He’s filled with love, that kid. Tina would often say to me, ‘He reminds me of a Brando,’ because there is something virile, animalistic, and sexual about him.”

In a family full of pent-up animosity, Phillip is the emotional blasting cap — and Driver served the same function on set, firing up his veteran costars with offbeat energy. ”He is frenetic, and he is moment-to-moment,” Levy says. ”When you say ‘Cut!’ he will not stay in the chair.”

If you need more evidence of Driver’s inability to sit still, consider his current film slate. In addition to this month’s What If (where he plays Daniel Radcliffe’s love-savvy pal), he’s got four movies in September’s Toronto Film Festival: This Is Where I Leave You, Tracks with Mia Wasikowska, Noah Baumbach’s While We’re Young, and the indie romance Hungry Hearts. ”That’s just too much of my stupid face,” Driver says. And in 2015, he has a mysterious role in Jeff Nichols’ sci-fi drama Midnight Special and will play a 17th-century Jesuit missionary in Martin Scorsese’s Silence.

But right now he’s still pacing — across an ocean this time, as he shuttles between England for Star Wars and New York City for Girls‘ fourth season. ”You can confuse the two,” he deadpans. ”I’m like…why is everyone naked in space?”