Philly homicide detective Virgil Tibbs (Sidney Poitier) has come to a small, prejudiced Mississippi town to visit family. Being a newcomer and an African American, he is immediately picked up when a rich Caucasian man is murdered. After the mix up is resolved, Tibbs is told by his boss to help with the investigation as the small town sheriff, Bill Gillespie (Rod Steiger), has no real experience with homicide investigations. The two have to learn to put aside their differences. Tibbs continues to be appalled by the deep rooted racism in the town. Together, Tibbs and Gillespie have to overcome the racial tensions in order to solve the murder.