Ryan Gosling in “Gangster Squad.” (Warner Bros.)

Penn plays gangster boss Mickey Cohen, a real-life mobster who has been played onscreen by Harvey Keitel (“Bugsy”) and Paul Guilfoyle (“L.A. Confidential.”) He’s come to L.A. to bring his mob mayhem to the city, which the LAPD’s Sgt. John O’Mara (Brolin) has been tasked with putting an end to.

And then we have Gosling, the light-eyed heartthrob of a thousand memes, as the slick-talking cop Jerry Wooters. “Doesn’t seem right that he should have so much, while others have so little,” Wooters says of Cohen, turning his eye to the dangerous man’s dangerously seductive girlfriend, played Emma Stone.

(While this is a “Crazy, Stupid, Love” reunion, I have a feeling this love affair may turn out differently.)

“Gangster Squad,” which also stars Nick Nolte, Anthony Mackie and Giovanni Ribisi, hits theaters in October. View the trailer in HD over at Apple.