The film stars Josh Brolin, Ryan Gosling, Nick Nolte, Emma Stone, Anthony Mackie, Giovanni Ribisi, Robert Patrick, Michael Peña and Sean Penn.

In 1949 Los Angeles, crime boss Mickey Cohen has become the most powerful figure in the underworld in California and intends to expand his criminal enterprise to encompass the entire West Coast.

The LAPD has not been able to stop his ruthless rise, as he has eliminated witnesses, hired dirty cops to protect his activities, and avoided prosecution through spreading corruption in the justice system.

The unit, composed of officers who do not carry badges and are authorized to act outside of the law, is led by the skilled World War II OSS veteran Sergeant John O'Mara.

Despite initial setbacks, such as a casino raid thwarted by corrupt Burbank cops, the Squad strikes several successful blows at the heart of Cohen's operations, including shutting down his lucrative wire gambling business.

The film explains that the Gangster Squad has never been mentioned for its role in keeping the underworld from gaining a foothold in LA, and that its surviving members remain extremely secret 'till this day.

Harris and Ramírez partner together to walk the beat, Wooters and Faraday continue their relationship, and O'Mara quits his job with the LAPD to live a peaceful and quiet life with his wife and newborn son.

[13] In the wake of the theater shooting in Aurora, Colorado, on July 20, it was pulled from running before films and airing on television, and removed from Apple's trailer site and YouTube due to a scene where characters fire submachine guns at movie-goers through the screen of Grauman's Chinese Theatre.

The website's critical consensus reads, "Though it's stylish and features a talented cast, Gangster Squad suffers from lackluster writing, underdeveloped characters, and an excessive amount of violence.

[21] Reviewers at Spill.com gave it a "Rental," praising its stylish design but criticizing the dialogue, Emma Stone's underdeveloped "damsel-in-distress" character, and Sean Penn's laughable makeup.

Filling in for Roger Ebert of the Chicago Sun-Times, Jeff Shannon gave the film 2 stars out of 4, saying that Fleischer, better known for his comedic work, was "out of his element, and barely suppressing his urge to spoof the genre".