In the early 1970s, Ron Stallworth (John David Washington) breaks barriers by becoming the first African American police officer in the Colorado Springs, Colorado police department. His initial role in the records room exposes him to the harsh realities of racism, facing slurs from his colleagues. Seeking a more impactful role, Stallworth requests to go undercover and is given the challenging task of infiltrating a local rally featuring the influential civil rights leader Kwame Ture (Corey Hawkins), born Stokely Carmichael. The police are apprehensive, fearing that Ture's presence could incite local African Americans to advocate fiercely for their civil rights.
During the rally, Stallworth encounters Patrice Dumas (Laura Harrier), the president of the African American student union at Colorado College. After the event, while driving Ture to his hotel, they are confronted by Officer Andy Landers (Frederick Weller), a corrupt and racist member of Stallworth's precinct, who threatens Ture and sexually assaults Patrice.
In the aftermath, Stallworth is moved to the intelligence division after reporting the incident to his chief, who dismisses his concerns due to his rookie status. While perusing the newspaper, he spots an ad for joining the Ku Klux Klan. Stallworth decides to feign being a white man and reaches out to the Klan's Colorado Springs chapter, eventually speaking with Walter Breachway (Ryan Eggold), its president. Aiming to attend Klan meetings in person, he persuades his Jewish colleague Flip Zimmerman (Adam Driver) to impersonate him.
As Zimmerman engages with Klan members including Breachway and the reckless Felix Kendrickson (Jasper Pääkkönen), he learns about a proposed attack from another member, Ivanhoe (Paul Walter Hauser). Meanwhile, Stallworth establishes a phone relationship with David Duke (Topher Grace), the Grand Wizard of the Klan and a presidential hopeful, further complicating their undercover mission. Tensions rise when Kendrickson suspects Zimmerman might be Jewish and threatens to expose him.
Amid growing tensions, Stallworth begins a romantic relationship with Patrice but keeps his police affiliation a secret. After providing crucial intelligence to the Army CID regarding active-duty Klan members, Stallworth discovers alarming ties to military personnel.
Their mission takes a perilous turn when Felix shows up at Stallworth's home. Thanks to Zimmerman's quick thinking and smooth talking, they evade danger. During Duke's visit for Stallworth's Klan induction, Stallworth is reluctantly assigned to protect Duke despite his protests. After Zimmerman's initiation, a deadly plot unfolds as Duke's invitation leads to a bomb threat that targets Patrice.
Once Stallworth realizes the gravity of the situation, he alerts law enforcement, managing to thwart the attack just in time. After a series of chaotic events, the plan fails spectacularly, resulting in tragic casualties among Klan members. Stallworth seizes the moment to gather evidence against Landers, ultimately resulting in the officer's arrest.
While Chief Bridges congratulates the team on their success, he insists on keeping the operation under wraps. However, Stallworth seizes his moment, revealing his identity to Duke before ending their deceitful conversation, bringing a sense of victory to him and his fellow officers. In a poignant conclusion, Stallworth and Patrice contemplate their future together but are ominously interrupted by a haunting symbol of racism—a distant flaming cross planted in the hills, as real footage from the 2017 Unite the Right rally plays, starkly highlighting the ongoing battle against hate and prejudice.
