In the early 1970s, Ron Stallworth becomes the first African-American detective to serve in the Colorado Springs Police Department. Determined to make a name for himself, Stallworth sets out on a dangerous mission: to infiltrate and expose the Ku Klux Klan. He initiates contact by responding to a classified ad in the local newspaper seeking new Klan members. Despite the obvious risk, Stallworth establishes a relationship with the hate group by posing as a white supremacist over the phone.

Stallworth recruits his Jewish colleague, Flip Zimmerman, to act as his white persona for face-to-face meetings with the Klan. With Stallworth orchestrating the investigation from the inside and relaying instructions to Zimmerman, the two officers delve into the murky world of white supremacy. Their audacious plan not only aims to thwart the Klan's violent activities but also to unravel the organization's ties within the town, including possible connections to the military and politics. As their investigation deepens, they are thrust into a perilous situation that threatens to expose their true identities and endanger their lives.