In December 1949, Marsha Mitchell, Ginger Rogers a dress model from New York City, travels by bus for a work assignment. During her journey, she stops in the small Southern town of Rock Point to visit her newlywed sister, Lucy Rice, Doris Day. Upon arrival, Marsha senses the townspeople's hostile stance, evident in their evasive and unwelcoming behavior. As she walks along the main street, she hears a disturbance at the nearby police station. Hiding in the shadows, Marsha witnesses an intoxicated, violent KKK mob break a man out of jail and fatally shoot him as he tries to flee. She observes two of the mob members unmasking themselves and sees their faces.
Deeply shaken, Marsha seeks refuge at the bowling alley where Lucy works. She recounts the events to Lucy, who surmises that the victim was Walter Adams, a journalist who had recently arrived in town and had been investigating and exposing the local Klan chapter's activities. Lucy explains that he had been arrested on false charges, and the mob had likely intended to silence him. Marsha is taken to Lucy's home, where she is encouraged to tell her brother-in-law, Hank Rice, Steve Cochran what she witnessed. However, when Hank arrives, Marsha immediately recognizes him as one of the unmasked Klansmen. Though Hank initially denies any involvement, he soon admits his presence at the scene, claiming he had been coerced and intoxicated. Hank insists that the mob's intention was not to kill Adams but to prevent him from further damaging the town's reputation. He pleads with Marsha to remain silent to protect his marriage and Lucy, who is pregnant. Reluctantly, Marsha agrees to leave town the next morning and forget what she witnessed.
Meanwhile, District Attorney Burt Rainey, Ronald Reagan begins an investigation into the murder. Skeptical of the police's explanation that they were overpowered by the mob, Rainey suspects collusion between the authorities and the Klan. He questions Charlie Barr, Hugh Sanders the Imperial Wizard of the local Klan chapter, but receives no useful information. Learning of Marsha's presence in town, Rainey insists on meeting her and questioning her about the incident. Despite pressure from the townspeople to drop the investigation, Rainey remains committed to pursuing justice. When Marsha meets with Rainey, she provides a partial account, stating that she saw the Klansmen but did not recognize their faces due to their hoods. Rainey deems this enough to proceed with the investigation and serves her with a subpoena to testify at the inquest later that day. Under pressure from both Lucy and the Klan, Marsha lies during her testimony, leading the coroner's jury to rule that Adams was killed by unknown assailants.
The Klan and its sympathizers celebrate at the local bowling alley, while Marsha, consumed by guilt, prepares to leave town. However, her departure is interrupted by a drunken Hank, who returns home and attempts to sexually assault her. Lucy intervenes, and denounces Hank, realizing the extent of his involvement. Marsha, now determined to tell the truth, declares her intent to report Hank's role in the murder to Rainey and the police. In a fit of rage, Hank kidnaps Marsha and takes her to a Klan rally, where she is beaten until Lucy, Rainey, and the authorities arrive to rescue her. Desperate, Barr attempts to shift the blame to Hank, naming him as the murderer. In the ensuing chaos, Hank seizes a gun, condemns the townspeople, and shoots Lucy. A police officer then fatally shoots Hank. As the remaining Klansmen, disillusioned, flee the scene and discard their robes, Barr is arrested. Lucy dies in Marsha's arms beneath the smoldering remains of a burning cross.
