Fred Hampton (Daniel Kaluuya) is the passionate chairman of the Illinois Black Panther Party. His activity gets the attention of the FBI, so when William O'Neal (LaKeith Stanfield) gets into trouble with the law, agent Roy Mitchell (Jesse Plemons) offers to get the charges dropped in exchange for William becoming an FBI informant.

O'Neal poses as a Black Panther follower and helps the FBI get into Hampton's inner circle, but his situation becomes dangerous when the Black Panthers suspect there's a rat in their midst.