In 1949, in the aftermath of World War II in Los Angeles, gangster Mickey Cohen (Sean Penn) has his sights set on dominating the entire West Coast. A brutal figure with a background in boxing, Cohen has ruthlessly ascended the ranks of the mob, amassing control over every illegal business within the city. His methods are as violent as they are insidious, involving the elimination of witnesses and corrupting law enforcement officials. For instance, to send a clear message to potential rivals, he gruesomely tears a Chicago mobster apart using chains attached to pick-up trucks.
Amidst this chaos, "Sarge" John O'Mara (Josh Brolin), fresh to the city, intervenes when he spots a young woman being assaulted by Cohen's thugs. Unbeknownst to him, the men he confronts are part of Cohen's operation, which preys upon innocent girls and coerces them into prostitution. Like Cohen, O'Mara embodies a certain ruthless ferocity, as he confronts these men head-on, breaking bones and, when necessary, bringing about fatal outcomes. Unfortunately, those he arrests find their way back to freedom almost immediately due to their connections.
O'Mara quickly suspects that a mole lurks within the police force, feeding Cohen information. In retaliation for O'Mara's interference, Cohen feigns forgiveness towards his henchmen but then coldly incinerates them in an elevator. He even sets fire to an entire building for insurance payouts. Karl Lennox (Holt McCallany), Cohen's bodyguard, further enforces the gangster’s stronghold.
Despite widespread caution from fellow officers about confronting Cohen’s nefarious gang, Chief Bill Parker (Nick Nolte) recognizes O'Mara's unique skill set gleaned from his special operations training at Camp X during the war. He empowers O'Mara to assemble a team to engage in a covert war against Cohen's empire, declaring that their normal police means would never succeed against such a formidable opponent. Parker’s intention is not to assassinate Cohen but rather to cripple his operations enough to force him out of the city.
To aid O'Mara, the pair gather a mix of seasoned misfits and wild cards. Coleman Harris (Anthony Mackie), who desires to combat Harlem's rampant drug issues, joins their ranks, alongside Conway Keeler (Giovanni Ribisi), the lone member with a child. Notably, there’s a sharpshooter named Max Kennard (Robert Patrick) and his quirky partner "Christmas", also known as Navidad Ramirez (Michael Peña), who seeks to prove himself.
As the action unfolds, Sgt Jerry Wooters (Ryan Gosling](/actor/ryan-gosling)), who shares a childhood bond with Jack Whalen (Sullivan Stapleton)—Cohen's bodyguard—becomes entangled in this explosive world. O'Mara's spirited wife, Connie (Mireille Enos), expresses her concern about her husband's latest venture, fearing it may lead to another violent war.
The stakes escalate when O'Mara and Harris decide to raid one of Cohen's casinos, only to be captured by corrupt officers, leading them to be mistaken for vengeful agents from Chicago. As Cohen grapples with rivalries and the fallout of his violent decisions, he finds himself at odds with Jack Dragna (Jon Polito), the head of a conflicting mob faction, further complicating the path to his dominance.
When Wooters engages with Cohen’s etiquette coach and love interest, Grace Faraday (Emma Stone), an intense romance blooms, adding another layer of complexity to this web of crime and loyalty. Their relationship, though initially secretive, is fraught with danger, especially as Cohen's violent tendencies begin to unravel more lives.
The relentless pursuit of justice leads to heroic encounters against Cohen's operation, shaping the squad into the Gangster Squad—a name that will remain a covert badge of honor as they face setbacks and betrayal. High-stakes firefights, heart-wrenching decisions, and harrowing confrontations ultimately culminate in O'Mara challenging Cohen to a bare-knuckle boxing match, a battle that draws a crowd of onlookers and media alike.
With a final stand where O'Mara prevails, he brings Cohen's iron grip on the city to an end, successfully arresting him and dismantling an empire built upon crime. Yet, even in victory, whispers of the squad's true accomplishments remain buried. As Cohen faces a lifetime behind bars, O'Mara chooses a quiet life with his family, and Wooters continues his relationship with Grace, forming new bonds amidst the debris of their tumultuous struggle.
