Shortly before America enters World War I, the Winfield family move into a new neighborhood. Although they now have a bigger house, no one is happy about the move but Mr. Winfield. His wife complains that nothing fits; the curtains are too short and the carpets aren't wide enough. Their children, eighteen-year-old Marjorie and eleven-year-old Wesley, are also grumpy. The maid Stella reports that the kitchen is too big and she won't be able to get food to the table while it's still hot. Mr. Winfield ignores their pleas to move back to their old house. He spots a neighbor boy outside and orders Wesley to introduce himself and be friendly.
The boy, Jim Sherman, claims that his father has a pistol once used to shoot outlaw Jesse James. Wesley asks to see it. They retrieve the pistol and go into the Shermans' barn to shoot it. But it won't work. Marjorie, who has joined a baseball game, sees the boys enter the barn and runs to stop them from getting hurt. She grabs the pistol from Wesley and tries to put the safety device back in place. Outside, a handsome young man is calling for Jim, obviously his brother because he shouts that their mother is looking for him. Marjorie accidentally fires the pistol, narrowly missing the young man and blowing the barn doors off. Jim gasps that his brother is dead. But although knocked down, Bill Sherman is very much alive. The boys run off, leaving Marjorie to face the music. Because she is wearing a baseball uniform, Bill mistakes her for a boy. But when he turns her over his knee and spanks her, he realizes she is a girl.
Later that evening, Bill comes to take Marjorie dancing at a local resort, Moonlight Bay. It is tomboy Marjorie's first date and she is uncomfortable in a dress and high heels. Her mother insists that she pad her bust with powder puffs. But while the two are dancing, the puffs fall out. Marjorie is very embarrassed and feels the evening is ruined. They stop at a carnival booth, where Bill declares he will win her a Kewpie doll. But he cannot throw and misses the pins. Marjorie takes over and manages to knock down all the pins, winning a doll for herself. When Bill takes her home, she invites him inside for a glass of buttermilk. But the lights go out and in the dark, she experiences her first kiss.
Some weeks later, Mr. Winfield is annoyed because Bill is at the house all the time. He decides to ask the young man his intentions. Bill and Marjorie are sitting on the front porch, playing records and singing. Wesley is under the porch, mimicking Bill in a high-pitched whine. Marjorie stomps on the floor and dust covers Wesley, who reluctantly crawls out. He leaves when Bill gives him money for candy.
Mr. WInfield joins the couple and at first is pleasant. But when Bill declares his disapproval of bankers, an embarrassed Marjorie tells him that her father is vice-president of the local bank. Bill apologizes but Mr. Winfield orders him to stay away. He encourages Marjorie to date Hubert Wakely, a boring, priggish young man who is also Wesley's piano teacher. But Marjorie can't stand him.
Bill returns to college but the two write to each other. Just as she is finishing a letter to Bill, Wesley realizes he was supposed to compose a letter to a friend on a general subject, for a homework assignment. When Marjorie leaves the room, Wesley takes her letter and signs his own name. Unfortunately, the teacher, Miss Stevens, decides to have the students read their letters aloud. Wesley begins with confidence, then his voice trails off as he realizes it is a steamy love letter. The other students laugh and the teacher makes him sit on a stool the rest of the day. He decides to get even with Marjorie, even though she had done nothing to him.
When Hubert Wakely comes to call, Wesley sits in the parlor with them. Hubert hints for him to leave, but he claims to be looking for his dog. At last Hubert asks Marjorie to take a walk, but Wesley follows them. It is nearly dark when they return and an exhausted Hubert takes himself off.
Unknown to Bill, Marjorie begins taking dance lessons so she can learn the latest steps. Bill is coming home from college and they plan to attend the big Christmas dance. On her way home, Marjorie is accosted by several boys who throw snowballs at her. She chases after them and trips over a garbage can, badly spraining her ankle. Sadly, she telephones Bill and tells him she can't go to the dance after all. She is too embarrassed to tell him why, and believes he will not come home.
Wesley is to be an angel in a group of carolers, directed by Hubert Wakely. His mother, Stella, and Marjorie make him try on his costume, complete with wings and a halo. Suddenly he realizes that it was made from an old petticoat of Marjorie's. He tears off the costume, breaking his wings, and yells that he will not be an angel because everyone will recognize Marjorie's old petticoat. He escapes his father's ire and takes refuge in a movie theater. The silent picture is about a respectable husband and father who is forced into a saloon and gets drunk. Staggering home, he beats his wife and daughter, throwing them out of the house into the snow. Then he has a change of heart, begging them to forgive them and swearing that he will never drink again.
The next morning, Wesley falls asleep in class and dreams he is flying about the room. His friends applaud him, especially when he shouts at Miss Stevens to leave him alone. Suddenly he wakes up and realizes Miss Stevens is standing over him. His friends are not applauding but laughing. Wesley is in big trouble and has to stay after school. He feeds Miss Stevens the plot of the movie, substituting his real family for the actors. The reason he fell asleep in class, he says, is that he was up all night taking care of his mother and sister after they were beaten by his father Miss Stevens is moved to tears and assures him that she understands.
The next day, Mrs. Winfield reports running into Miss Stevens and having the teacher take her hand. She found it quite embarrassing when Miss Stevens told her to take courage, that everything would be all right. Miss Stevens also says that she is sure Wesley is a great comfort to Mrs. Winfield. No one can understand any of it and Mr. Winfield thinks Miss Stevens may be going senile.
Later that evening, Stella applies rubbing alcohol to Marjorie's leg. Since Wesley still refuses to wear his angel costume, his father orders him to bed. He falls asleep on the sofa and Mrs. Winfield spreads a newspaper over his face, to keep out the light. Suddenly there is a persistent knocking at the door. It is Bill, home from college. He strides over to Marjorie and, on seeing her injured ankle, announces that it is true. He didn't believe any of it, even after what Miss Stevens told him about Mr. Winfield drinking and beating his family. The Winfields are bewildered and Wesley, lingering on the stairs, knows he is about to be found out. Bill says he can smell alcohol and Marjorie shows him the bottle of rubbing alcohol. Bill is so disgusted that he throws it into the fire, causing a big blaze. Before anyone can stop him, he grabs a picture of water and pours it on Mr. Winfield, accusing him of being a drunken brute. Marjorie screams at him to get out, that she never wants to see him again. Stella threatens him with a mop and Mrs. Winfield asks if he has lost his mind. Before being propelled through the front door, Bill says that Miss Stevens told him the whole story, which she had gotten from Wesley.
Suddenly the family realizes what must have happened. Marjorie hobbles outside, begging Bill to come back. Mr. Winfield goes looking for Wesley, intending to give him a sound spanking. But his son is missing. Bill accepts Marjorie's apology and they kiss. Just then the carolers come down their street. Wesley is on the front row, wearing his costume with its broken wings. He looks so innocent that his parents decide not to punish him.
In the spring, the Winfields attend Bill's college graduation. He hints that he has a surprise for Marjorie but won't tell her what it is, adding that she will know soon enough. Mr. Winfield has come to accept Bill and asks Marjorie if they will be setting a date soon. When she replies that he doesn't believe in marriage, Mr. Winfield is shocked and then angry. He forces the family to leave the ceremony, even though Bill, as valedictorian, is making a speech. At the end of it, he and the other graduates remove their robes. They are wearing army uniforms, having just enlisted. Even that doesn't move Mr. Winfield. He orders Marjorie never to see Bill again.
Time passes and Marjorie continues to grieve for Bill. With her father's encouragement, Hubert Wakely begins calling on Marjorie again. Mrs. Winfield says that Marjorie can't stand him, but Mr. Winfield believes that will change. Best of all, Hubert was turned down for the army because of his punctured ear drum. Stella makes a crack about him having punctured it just before his physical.
Jim Sherman asks if Wesley can go to the train station with him, as a troop train carrying Bill will be passing through. Mr. Winfield says no. Wesley grumbles that he doesn't see why he can't go, since Marjorie is going. His parents are shocked to learn that Wesley saw her packing a suitcase. Realizing that she intends to elope with Bill, Mr. Winfield hurries to the station to stop her.
Marjorie searches the cars until she finds Bill. She declares her intention of going with him, no matter what her father says. She will get a place to live near the army camp. They go outside and he proposed marriage to her. She accepts and he tells her to get the next train to Chicago, where he will meet her and they will be married at once. But Mr. Winfield appears and tears Marjorie away, telling her she is coming home to grow up.
Wesley apologizes to Marjorie for telling on her and she says it doesn't matter now. Bill is gone and it will be a very long time, if ever, before she sees him again.
The Winfields throw a party for Wesley to celebrate his twelfth birthday. Their elderly Aunt Martha arrives and gives him three presents; a box of home-baked cookies and a pocketknife. The last is a slingshot. Aunt Martha explains that she took it away from Wesley's father thirty-five years ago, when he was twelve, after he killed her best laying hen. She thinks maybe he can be trusted with it now. The party is a wash-out, since Hubert Wakely is in charge of the entertainment and bores the children by playing and singing. Wesley is mad because he couldn't have the sort of party he wanted, and after a while slips away.
Meanwhile, Bill comes to the back door and asks for Marjorie. He has an unexpected pass home, but can only stay a short time. Marjorie rushes into his arms and Mr. Winfield reminds him that he is not welcome in their home. Marjorie asks for and receives permission to walk to the gate with him. Meanwhile, Mrs. Winfield confronts her husband. She reminds him that Bill is a great deal like himself as a young man. Marjorie comes in and rushes upstairs, sobbing. Wesley uses the slingshot, only it breaks and sends the stone crashing through the front window. Mr. Winfield is furious until Wesley tells him what Aunt Martha said. He had forgotten the incident and ponders briefly. Then he goes to the phone and calls the Sherman residence, asking whoever answers to tell Bill that his across the street neighbor suddenly remembered that he was young once. Marjorie overhears and after kissing her father, rushes outside. Bill meets her halfway and they embrace. Hubert Wakely, on his way out, realizes he has lost Marjorie once and for all. Wesley hands him his hat and Hubert jams it on his head. The brim has been cut and the hat is ruined. Wesley smiles and looks at his pocketknife as Hubert stalks angrily down the street.