The O’Leary family moves to Chicago where two brothers become a lawyer and a gambler and rivals. In 1871 a fire devastates much of the city.
In 1854 a covered wagon is crossing the prairie in the Midwest. Patrick O’Leary (J. Anthony Hughes) is driving and conversing with his wife Molly O’Leary (Alice Brady). He expects to rest in Chicago that night. They have three young boys, and one urges his father to race a passing train. The two horses run as fast as they can, but they go over rough land. Patrick is thrown off the wagon and is dragged on the ground. Patrick and the boys run after him. She sends Jack to fetch water, and the youngest boy is crying. She uses a cloth and water to daub the wounds on his head. He says it is the devil’s doing. He asks his boys to come closer and tells them Chicago is “a grand new place.” He urges them to boom with the city. He says it is his last breath and asks them to bury him there. He dies.
Their wagon arrives in a muddy street in Chicago. Molly is looking for a job before they get a place. She sees a sign “Girls Wanted” and goes in. The boys see four ladies riding on a carriage that gets stuck in the mud. They go to carry them from the carriage to the sidewalk. Two boys lock arms and carry one lady. Molly comes out and calls to them, and they drop a lady in the mud hole. The woman says no washer woman could save her dress, and Molly says she can do it and will name her price.
Molly washes clothes as years pass to 1867. Molly now has a French laundry with a wagon. She is taking clothes off the line and tells Bob O’Leary (Tom Brown) to wash up. He goes into the barn where Gretchen (June Storey) is milking their cow. The cow kicks over the pale of milk, and Bob tells her she should put the bar between the cow’s legs to prevent that. He hugs her, and they kiss. They enjoy it and kiss again. Jack O’Leary (Don Ameche) is carrying a book and talks to Molly about his law case in court. He complains about the politician Gil Warren. He says decency is needed to make the city the best. Dion O’Leary (Tyrone Power) gets out of a police van and hugs his Ma. Jack admits the judge dismissed his case, but Dion says he had the court hypnotized. Pickle Bixby (Andy Devine) says all but the judge. Dion tells his Ma to quit the laundry business and offers to set her up in town. He shows her a roll of money and admits he was gambling. She refuses to accept dishonest money. They find a table cloth with a map drawn on it. Jack figures out they are going to run the car line by Randolph Street. They realize they have valuable information that could help them invest and make money. Dion says he would put up the biggest saloon in town. He sees the name “B. Fawcett” and cuts it out. He tells Pickle they are going to check it out.
At The Hub where Gil Warren is the proprietor bare-legged women are dancing on stage. Dion with Pickle asks to talk to Gil Warren (Brian Donlevy). He tells them to wait while he listens to Belle Fawcett (Alice Faye) sing “Carry Me Back to Old Virginny.” Gil tells them she was a sensation in New York, and he is paying her more than any other woman in town. She says the proceeds this night are going to the family of the man who was shot by the door. She conducts an auction, and Dion offers $100 if she will play Venus. He hands her the cash, and she puts it between her breasts. Gil has Dion thrown out in the alley.
Later Belle comes down stairs and gets in her carriage. Dion is there and won’t let her out. She struggles, and he confesses he is in love with her. She threatens to call the police if he does not get out. She does not know him but suggests he buy her a drink. He asks her to take him to her place. They get out, and she pushes him into a water trough and leaves in the carriage.
Jack comes in and tells his Ma he won his first case. Dion asks how much he got. Jack says his client was too poor to pay him. Molly complains about her two oldest sons. Dion goes out.
Belle has a colored maid who helps her take off her dress. Belle sees Dion in her mirror and throws things at him. He grabs her, and she calls for help. The maid comes in and goes out. While they are laying on the floor, Dion kisses Belle. He says he loves her and says they could make money on the property she owns. She says she is a business woman, and they kiss. The maid comes back with a policeman and says the fire is out.
Dion and Belle open a place called The Senate. Young women are dancing on stage. Dion welcomes people, and Pickle tells men to take off their hats. On stage Belle sings “In Old Chicago” and dances with the women, lifting her dress. Dion meets Senator Colby (Berton Churchill) and his daughter Ann (Phyllis Brooks). Dion sees Gil and asks if he is sore. Gil wants to talk to Dion, and they go in his office. Gil says times have changed. He says he wanted to marry Belle but does not resent Dion taking her. Gil says he is going to run for mayor and asks for his help. Gil offers to close The Hub if they work together politically. He says they can run the town. Gil hands Dion a check for $10,000, and Dion says they will manage well. They go to the bar for a drink, and Gil greets Belle. Her music starts, and she sings “I’ll Never Let You Cry” with a male quartet. Dion sits at a table next to Ann and gazes at Belle. She takes Dion away from Ann. In her room Belle warns Dion about taking Gil’s money. Dion says he will vote for Gil but will use him. He takes her in his arms and asks if she loves him. She asks about the other woman. They kiss.
Six men have come and ask Jack to run for mayor for the Reform Party. They say he will win, but Jack says he cannot count on his brother. Jack agrees to run. The six men go back to Dion, and they laugh about what happened.
Dion and Jack play pool and talk about the campaign. Jack warns Dion he might go after him to make Chicago a good city. Dion gives Jack twenty cents for the two games he won.
Molly plays the organ and sings with her three sons and Bob’s wife Gretchen. They present her with a picture of their father. Molly shows the picture to her grandchild. Dion kids her that his father had a roving eye for the women. They give Molly beer to drink, and she plays a jig for the other four to dance. Jack says he met Miss Fawcett, but Molly does not want to meet her. Molly tells Dion she wants him to bring her a sweet woman and grandsons. Dion takes Ma for a ride, and Belle is in the carriage. Molly objects and quarrels with Belle, but Dion won’t let them out. Belle says she will be his wife, and Molly says he will never marry her. Molly gets out, and Dion apologizes to Belle.
In front of a political sign Jack gives a campaign speech promising to clean up the Patch or wipe it out. Dion and Belle listen from a carriage. Dion tells her that Warren’s supporters may not show up on election day. Dion tells his employee he paid in cash by different people he must undermine Warren.
Gil Warren leads a political parade in the street with a band and many signs. Dion walks next to him. Inside a saloon bartenders pass out free beer to the Warren supporters. Gil dances with Belle and says he will be mayor.
Outside a commissioner sees that things are ready. He goes in, and Pickle nods to Dion. Pickle starts a fight that turns into a brawl. Gil tries to stop it, but it spreads. Police rush in with clubs and hit men. Dion leaves with Belle, and she warns him about the Colby woman.
Gil goes to the police chief and tries to see the judge, but he is not there. Gil goes to Dion and asks what they should do. Dion says he sold him out, and Gil is through. Dion says he is going to vote for his brother.
From a window Gil watches Jack with his Ma celebrating his victory. Dion is glad his mother feels great.
At the Senate a man sings. Pickle shows Dion a newspaper that says Jack has declared war on the Patch. In her room Jack tells Belle that he is going to clean out the patch, and he wants her help. He wants to wipe out the vice and crime. He can condemn the property by the right of eminent domain. She says she and Dion have their money tied up in the Senate. Jack wants to see them married. She agrees. Jack says he will start an investigation. Dion walks in and says he heard. Dion says he elected Jack and sent the committee to him. Belle confirms it is true. Jack asks Dion why he made him mayor. Dion says he is Chicago and may have to kick Jack out. Belle backs up Jack, and Dion says he won’t be seeing her much and goes out. She is upset and cries.
A newspaper reports a grand jury investigation that has subpoenaed Belle. Her maid helps her get ready. Dion comes in, and Belle throws things at him. He struggles with her, and the maid goes for help. He holds Belle against a wall and says he loves her. He asks her to marry him tonight. They can go to Jack. They kiss, and the maid arrives with a policeman.
Jack is speaking to a group of men and talks about the menace to Chicago that must be cut out. He gets a message and goes out to talk to Dion and Belle. Dion says he has been a fool and that Jack has won. Dion asks him if the Mayor can marry them. Jack finds out, and in a small ceremony before three witnesses he declares them husband and wife. Jack suggests they tell Ma. Dion says Belle cannot testify against her husband, and he laughs. Belles rushes out, and Jack slugs Dion. They fight, and Jack knocks out Dion. He pours water on him. Jack says he will wipe out the Patch. Jack tells Dion to get out, and he orders his servant to get the police and a reporter.
Molly watches a calf feeding from her cow. She goes out, and the cow kicks over the lantern. Molly and Gretchen learn about the fight. A man sees a fire in the barn, and the word spreads. The fire alarm is rung, and the firemen and others try to put out the fire with water. The fire spreads quickly among the wooden buildings. Molly, Gretchen, and the baby leave in the carriage.
Pickle tells Dion at the Senate about the fire. Men say the Mayor is burning them out. Dion goes to fight Jack. Gil is cynical about the O’Leary brothers. He tells men to get the boys together at the armory.
The streets are crowded with people trying to leave and with fire trucks. The flames are huge and are spreading. Dion searches. At a distant building Jack consults a general and gives orders to contain the fire. The maid wakes up Belle. Dion finds Bob and is looking for Ma. Bob says it started in their barn, and Dion blames it on Jack. A fire truck frightens Ma’s horse, and it runs off. She and Gretchen get out of the wagon. Ma goes back for the picture and is separated from Gretchen in the crowd. The General orders a block to be evacuated so they can dynamite. Dion and others are pushed back by the police. Dion sees Jack and runs out. The police stop him. Jack is angry at Dion. Bob tells Jack men are organizing against him because they think he started the fire. Dion says their house is burned. Dion sees Gil Warren and his gang coming. Jack orders the police to keep the people back. Dion tries to explain to Gil that Jack did not start the fire. Gil says it is an O’Leary trick. Gil refuses to let them dynamite their homes to save other homes. Dion runs off, but Gil throws a rock that brings down Dion. Jack goes to Dion, who tells him to light the dynamite. Jack grabs a torch and lights the fuses. Gil sees him and says to kill him. A man shoots Jack, and he falls. Gil tells his men to put out the fuses. The mob breaks through the police line. Bob tends to Dion who asks about Jack. They see the buildings being blown up.
In the stockyards cattle break out and stampede in the streets. Gil tries a door that is locked and climbs up the wall; but a board comes loose, and he falls in front of the cattle. A ship captain warns that a warehouse will blow up and burn the north side. People try to go to the lake. Bob struggles to get to Gretchen. Molly sees people trample on her picture. Belle helps Molly, who refuses her help. Belle helps Molly, who tells her that Dion loves her. Belle asks for help as people rush by. People go into the water to escape from the flames. Dion wades in the water looking. He tells Bob that he did not find them on the north shore. He is going to the south shore. Dion searches among the crowd. Finally he sees Ma on the lake in a wagon with Belle. Ma asks about the others, and she learns that Jack is dead. She is glad that they made it up. Dion embraces Belle. Molly and Dion say that Chicago will come back.
This romantic drama portrays a family with two capable men who become influential in the growing Chicago. One is a romantic gambler who manipulates others, and the other is a reforming lawyer who wants to improve society. Their different values bring them into conflict even though they like to help each other. The fast-growing city is exciting, but the fire takes its toll.