After fifty years of guilt over his brother's brutal murder in Civil Rights-era Mississippi, Warren Williams decides to renew his fight to bring the men responsible to justice. His efforts put him face-to-face with one of the murderers, Earl Olsen, in a remote Ontario town, where a contest of wits will end in death.

One Night in Mississippi is the story of a young activist named Graden Williams, who was brutally murdered in Mississippi during the sixties. After the perpetrators were charged but quickly released, Graden's brother, Warren, drifted aimlessly for decades, estranged from the rest of his family and struggling with guilt over his brother's death. But when the U.S. Justice Department begins re-opening cases like Graden's more than forty years later, he dedicates himself to bringing Graden's killers to justice.

A phoned-in tip after a television appearance leads Warren to a remote town in northern Ontario, where he meets Earl Olsen, the only murderer still at large, who turns out to be very different than what Warren had expected.