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Model Marsha Mitchell takes advantage of an out-of-town assignment to visit her newly married younger sister, Lucy Rice.  On her arrival, Marsha is struck by the unfriendliness of the townspeople, and when the taxi driver refuses to drive her to her destination, she is forced to walk to the recreation center where Lucy has a night job.

On the way, Marsha secretly witnesses a lynching.  Greatly upset, she finally reaches the recreation center and tells Lucy what she saw.  Lucy realizes that the victim must have been Walter Adams, a reporter who had denounced the Ku Klux Klan.  Although Marsha recognizes some of the men at the center as part of the lynch mob, she does not expose them when county prosecutor Burt Rainey questions the crowd.

Later, Lucy, who is pregnant, takes Marsha home and introduces her sister to her husband Hank.  Aghast, Marsha realizes that Hank was also one of the mob.  When Lucy tells Hank what Marsha witnessed, he explains that he thought they were only going to try to scare Adams.  Not wanting to hurt her sister, Marsha plans to catch the first bus out of town in the morning.

A worried Hank then hurries to the recreation center to confer with Charlie Barr, his boss and the Klan leader.  Rainey returns, having identified the rope used to hang Adams as belonging to Barr's company, but Barr dismisses Rainey's accusations; George Athens, the recreation center proprietor, testifies that Barr was there the entire night.

Rainey is waiting for Marsha when she picks up her suitcase the following morning.  Marsha claims not to know anything, but when she inadvertently reveals that the killers were wearing Klan hoods, Rainey orders her to stay in town for the inquest.  Barr then warns Marsha not to blame the Klan when questioned under oath, because Hank killed Adams and will hang for murder. M arsha begs Lucy to leave her husband, but she is too much in love with him to listen to Marsha's pleas.

At the inquest, no one, including Marsha, will testify about the previous evening's events, and Adams' death is attributed to unknown assailants.  Rainey, who is also getting community pressure to let the matter drop, tells Marsha that she has just given the Klan license to write their own laws.

Later, a drunken Hank comes home while Marsha is alone packing and tries to force himself on her, but Lucy interrupts and finally agrees to leave with Marsha.  Now Marsha resolves to testify against the Klan.  Hank beats her, and later, the Klan brings her before the membership to be punished.  Lucy brings Rainey to the meeting, and a gunfight ensues.  Hank shoots at Marsha, but accidentally kills Lucy.  After Barr is arrested, the mob panics and runs away.  Although the Klan's power is broken, Marsha blames herself for the death of her sister.