Entertainment Tonight ET Online ETOnline.com

Ryan Gosling and Emma Stone are bringing their Crazy, Stupid, Love chemistry to the period mob drama Gangster Squad, in theaters this fall, and we have a first look behind the scenes and at the film's exciting trailer!

"We get a little goofy around each other, so it was hard for us to be dramatic and be serious," says Ryan of working again with Emma. "But by hook or by crook, I think we kept a lid on it."

Video: Steve Carell and Ryan Gosling On Partnering Up For 'Crazy, Stupid, Love'

"Well, I'm the luckiest girl in the world because [the character of Wooters] is being played by Ryan," says Emma. "So, that is a huge asset, because he's so fantastic at that kind of banter, and we get along really well, and so it's been nice to kind of have that teammate, that partner."

Sean Penn, Josh Brolin, Nick Nolte, Robert Patrick, Michael Peña, Giovanni Ribisi and Anthony Mackie also star in the late '40s drama that chronicles ruthless, Brooklyn-born mob king Mickey Cohen's (Penn) domination of Los Angeles – and the super-secret crew of LAPD outsiders recruited to stop him.

Cohen rules the City of Angels by controlling the drugs, the guns and prostitutes and, most importantly, the police and the politicians. Now, it's up to Sgt. John O'Mara (Brolin) and Jerry Wooters (Gosling) to try to tear Cohen's world apart and take back the town from one of the most dangerous mafia bosses of all time.

Video: 'The Help' Star Emma Stone's 'Cornucopia of Drinks' Meeting

"[They have] to become more gangster than they are cops in order to beat the gangsters, in order to clean up the city," explains Brolin. "There's a [sense of] cool about the honor of who they were."

Watch ET for more with the stars of Gangster Squad.