In Hillsboro, State of Tennessee, high school biology teacher Bert Katz was arrested for violating state law by teaching Charles Darwin’s theory of evolution to students. This case immediately became a national incident and was called "Monkey trial" by the media. The well-known politician Matthew Harrison Brady will sue Burt, but the Baltimore Herald reporter E.K. Hernbeck hired Chicago lawyer Henry Drummond to defend Burt. In prison, Burt’s fiancée Rachel persuaded him to apologize and admit his mistake. Rachel’s father Jeremiah is a pastor and Bible missionary in the city. Rachel returned home and told her father that she would not leave Bert, who accused her daughter of betraying her faith.
Matthew Harrison Brady and his wife Sarah arrived in Hillsboro. After the mayor announced Brady as an honorary colonel, after Brady gave a speech, the crowd was excited. The next day, Drummond was greeted by several students from Hernbeck and Burt. Drummond was close friends with the Brady family. The courtroom began in hot weather. Drummond pointed out that propagating a later bible meeting in the courtroom might affect the jury, but Brady accused him of trying to tarnish the minds of young people. That night, Drummond attended the bible gathering of pastor Jeremiah. Jeremiah condemned Bert and urged the crowd to curse him. When his daughter Rachel begged him to stop, Jeremiah also began to curse her. Finally, Brady persuaded her. The masses remain tolerant and take care of Rachel to comfort.
After returning to the hotel, Brady and Drummond sat on the rocking chairs outside the door and asked how they became more and more alienated from their old friends, but they disagree. The next morning, Brady interrogated Burt’s students about his homework in court. Drummond asked the boy if the lessons corrupted him. Brady then used Rachel as a witness and asked her to reveal the reason why Burt had left his father's church, which she had told him in private, and Rachel couldn't say so much. Then Drummond began to defend, but the judge rejected all the experts who proved the theory of evolution as witnesses. Since there were no witnesses, Drummond angrily asked the court to allow him to resign and accused the court of prejudice. The judge condemned him to contempt the court.
In the evening, the people in the town demonstrated that they would burn Burt to death. Hernebeck said to Drummond that the crowd was still a group of apes. Drummond got inspiration from the hotel’s bible, and the next morning he apologized to the judge and asked the prosecution lawyer Brady to be a witness. Brady believed in his beliefs and asserted that every word of the Bible is true. Drummond was going to prove that Darwin and the Bible were not incapable of coexistence. When Drummond asked him how he knew God was not talking to Darwin, Brady blurted out and God told him. Drummond took the opportunity to shout that Brady thought Being a prophet, Brady left the witness stand trembling.
In the evening, Rachel went to visit Brady, but Sarah persuaded Rachel to trust Bert, just like Sarah believed Brady. The next morning, in the court Rachel returned to Burt, waiting for the verdict. The jury unanimously convicted Burt, but the judge was hinted by the mayor to end the case as soon as possible, and finally sentenced him to a fine of $100. After the case was over, Brady still wanted to give a speech in court, hoping to regain the love of the masses, and fell to his death in too much excitement. In the obituary of Hernbacher Plan Brady, Drummond quoted the Bible to defend the fact that Brady was once a great man. Hernbeck realized that Drummond was not an "agnostic" but also a Bible. Believers, condemned him as a hypocrite. Drummond answered him. After Hernbeck left, Drummond packed up his luggage and left, holding the Bible and Darwin's books in his hand
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