The titles appear as a young child babbles while picking through childhood mementos found in a cigar box.
An adult woman is recalling formative events of her childhood in the small Alabama town of Macomb, that was "a tired old town even in 1932" when she "first knew it." They had recently been told they "had nothing to fear but fear itself," which refers to FDR's inaugural address of March 1933. She was six years old that summer.
Jean Louise "Scout" Finch (Mary Badham), wearing bib overalls and her hair in bangs, greets Walter Cunningham, a farmer who is dropping off some hickory nuts. She summons her father Atticus (Gregory Peck) to thank him. When Mr. Cunningham leaves, Atticus explains that he is embarrassed to have to pay for "some legal work" in this way.
Their cook Calpurnia (Estelle Evans) wants Scout's older brother Jem (Phillip Alford) to come in for breakfast, but he is in a sulk because Atticus says he is "too old to play football for the Methodists." Miss Maudie (Rosemary Murphy) across the street assures them that he is respected as a very skilled lawyer.
In the collard patch of their neighbor they discover a boy a little older than Scout. He is Dill (John Mosna), staying with his Aunt Stephanie for the summer. They tell him about the neighbor two houses away they have never seen. Jem describes him as a homicidal maniac of frightening appearance. Dill's Aunt Stephanie (Alice Ghostly) adds to the story.
At 5:00 o'clock they walk to meet Atticus, returning home, and pass by elderly Mrs. Dubose, who rails at them from her porch. Atticus handles her with his customary grace and sensitivity.
That evening, Atticus listens to Scout read aloud. When she asks about Boo Radley, Atticus reminds her that he has told them "to leave those poor people alone." They reminisce about her mother, who died when Scout was two and Jem was six. Judge Taylor (Paul Fix) comes to ask Atticus to defend in a problematic case involving a man named Tom Robinson. He is relieved and grateful when Atticus agrees to.
The next day, Dill dares Jem to go up to the Radley's porch. Jem can't avoid it when Scout, rolling in a loose tire, ends up at the foot of their steps. Then Dill wants to go to the courthouse to see where Boo Radley had been locked up. They end up looking in to the preliminary hearing concerning Tom Robinson. Tom is a black man who has been accused of raping and beating a young white woman. Bob Ewell (James Anderson), the girl's father, confronts Atticus in the hallway. He tells Atticus he is concerned that "people are saying you believed Tom Robinson's story agin ourn." He becomes quite hostile, but Atticus remains calm, and cold.
At night, Dill prompts Jem to look in a window of the Radley house. The shadow of a man in a baggy shirt looms over Jem, and the shadow of his hand reaches out to touch Jem. When Jem cowers in fright, the man quietly withdraws. The children flee. Jem's overalls get caught in the fence, and he has to leave them. Dill is called home, and he says, "See you next summer." When Jem goes back to get his pants, Scout hears a gunshot, but Jem returns safely. They go around to the street to find the neighbors in an uproar because Mr. Radley had fired to frighten "a prowler." Atticus calmly says the excitement is over.
On her first day of school, Scout feels very awkward wearing a dress. She has a rough first day, and gets in a fight with young Walter Cunningham, Jr. Jem breaks up the fight and invites Walter to have lunch at their house. Jem learns that Walter has his own gun, and hunts rabbits and squirrels with his dad for food. Atticus tells of getting his first gun, when his father told him it was "sin to shoot a mockingbird," because it does no harm, but only sings. Scout is appalled when Walter drowns his plate in syrup, but Calpurnia gives her a lecture on hospitality. That evening, when she complains about school, Atticus teaches her about empathy and compromise.
Jem and Scout learn more about their father's stature and hidden gifts when Sheriff Heck Tate (Frank Overton) relies on Atticus to shoot a rabid dog on their street.
Both children ask to go with Atticus when he visits Tom Robinson's wife, Helen. Waiting in the car, Scout falls asleep, but Jem is frightened when drunken Bob Ewell lurches against the window, and calls Atticus "nigger lover." Atticus reassures Jem, "He's all bluff," and says that he wished he could keep the ugly things in this world away from them, but knows that is not possible. When he drives Calpurnia home, Jem waits nervously, listening to the spooky night sounds.
Scout continues to have fights at school, because people denigrate Atticus for defending a Negro. He explains that he has to defend Tom Robinson, or he could not hold his head up in town. He tells her she must not fight, no matter what people say.
In a hole in a tree in front of the Radley's, the children find two carved figures that look just like them. Mr. Radley appears and cements up the hole. That night, Jem shows Scout a cigar box filled with all sorts of little gifts that he had found in the tree. He tells her how the night he went back to get his "britches" he had found them "folded across the fence."
When summer comes, Dill returns. And it is time for Tom Robinson's trial. He has spent the year in the Abbotsville jail, because the Sheriff thought he would be safer there. Now he is back at the town jail, and Heck Tate expects trouble. Atticus takes a reading light, and leaves. Jem wants to check on him, and he and Scout and Dill walk downtown. Atticus is reading in a chair on the jail porch. Suddenly, numerous cars arrive, and men with rifles approach. The children push their way forward. Jem refuses when Atticus tells them to go home. There is an impasse, until Scout recognizes Walter Cunningham, and engages him, which leads him to call off the lynch mob.
Next morning, crowds arrive to attend the trial, and the children go down to the courthouse. They are able to find a place with Rev. Sykes (Bill Walker) in the gallery, with all the black folks.
In the Sheriff's testimony Atticus establishes that Mayella Ewell (Collin Wilcox) was badly beaten on the right side of her face and had finger marks all around her neck.
Bob Ewell testifies that he returned to hear Mayella screaming, and that he saw who did it. Atticus has to tell him to remain for his questions. He asks why no doctor was called, and gets Ewell to write his name. The judge points out that this shows he is left handed. Ewell feels tricked.
Mayella testifies that she asked Tom to "bust up" a chifforobe in the yard, and that when she went in to get him a nickel he followed her and attacked her. Atticus asks her if her father got riled when he drank, and asks if he had ever beaten her. Mayella is extremely uncomfortable, and her testimony is inconsistent. When Tom (Brock Peters) stands to be identified, Atticus asks him to catch a glass he tosses to him. He establishes that Tom cannot use his left hand, as it was "caught in a cotton gin" when he was twelve. When he asks Mayella how Tom could have done what she claims, she breaks down.
The prosecutor rests, and Atticus calls Tom Robinson to the stand. Tom is dignified and articulate, but increasingly uncomfortable. He testifies that he busted up a chifforobe for Mayella "way last spring . . . way over a year ago," and refused the nickel she offered. After that he did lots of favors that she asked him to do, until one day she got him in the house and grabbed him and told him to kiss her. Bob Ewell "cussed at her from the window" and said he "was gonna kill her."
In cross examination, the prosecutor (William Windom) gets Tom to admit he is "strong enough to choke the breath out of a woman and sling her to the floor." He scoffs at Tom's helpfulness and says: "You felt sorry for her? A white woman?"
When Atticus sums up, he points out the lack of evidence and that Mayella was beaten by someone left handed. He says that he has pity for Mayella, "a victim of cruel poverty and ignorance," but cannot let her put a mans life at stake to cover her guilt at breaking the social code.
After "almost two hours" the jury brings back a verdict of guilty. The judge dismisses them and leaves, slamming his door. Atticus tells Tom that he had told Helen they would "probably lose this one."
All the white folks leave the court. The blacks in the gallery watch Atticus gather his papers. One by one, they all stand. Rev. Sykes says, "Miss Jean Louise, stand up. Your fathers passin'."
Back at home, Miss Maudie tells a disconsolate Jem that his father is one of those "men in this world who are born to do our unpleasant jobs for us." Sheriff Tate arrives and talks with Atticus, who then reports that Tom has been killed. A deputy had shot at him and had "missed his aim" when Tom "broke loose and ran . . . like a crazy man." He says that on appeal they would have had "more than a good chance."
Jem insists on accompanying Atticus to go tell Tom's family. Bob Ewell arrives and spits at Atticus, who calmly wipes his face and leaves.
Next October, Scout wears a ham costume in a school pageant. She wears it walking home with Jem after dark. They are attacked. Jem is thrown to the ground, but another man in a baggy shirt arrives and there is a struggle with their attacker. Scout cannot see well from inside her costume, but she sees the man in the baggy shirt carry Jem to their house. Scout gets home and finds Jem is unconscious, with a badly broken arm.
Sheriff Tate reports that Bob Ewell has been killed with "a kitchen knife." He asks Scout to tell what happened. Scout sees the man who rescued them behind Jem's door, and realizes it is Boo Radley (Robert Duvall). She takes him by the hand, and invites him to "say goodnight to Jem." When he hesitates to touch Jem, she reassures him that he "can pet him," since he is asleep. Boo strokes Jem's head gently.
Atticus, thinking Jem wielded the knife, begins to consider a case of self defense involving Jem, when the sheriff corrects him. He says decisively: "Bob Ewell fell on his knife." He implies that Boo must have killed Bob Ewell. He says he feels Boo did a civic duty "to do his utmost to prevent a crime from being committed," and that to "drag him into the limelight" would be "a sin." Scout agrees-- that it would be like shooting a mockingbird.
Atticus shakes Boo's hand, and says, "Thank you, Arthur, for my children." Scout walks Boo back to his front door.