In Prohibition-era Chicago, Al Capone has risen to power as the city's most notorious gangster, profiting massively from illegal liquor sales. The rampant corruption within the police force and politics makes Capone seemingly invincible, his criminal activities untouched by the law. To combat this, Treasury agent Eliot Ness is appointed to lead a task force to bring Capone to justice. Determined to enforce the law, Ness realizes that he needs to recruit a team beyond reproach to fight the pervasive corruption.

Ness assembles a small, select group of men who are 'untouchable', immune to the bribes and intimidation tactics that have compromised so many others. This team includes veteran officer Jim Malone, who knows the city's streets and Capone's underworld dealings; rookie cop George Stone, a sharpshooter with a personal vendetta; and the nerdy but resourceful accountant Oscar Wallace. Together, they form an incorruptible unit, launching raids against Capone's liquor caches and seeking any legal means to indict him. Their efforts disrupt Capone’s operations, but also provoke a violent backlash from the gangster’s enforcers, putting their lives and the mission in peril.