It is loosely inspired by the Great Chicago Fire of 1871. The O'Leary family, consisting of a widow and her three young sons, arrive in the booming city of Chicago in 1854. Molly O'Leary starts a laundry business. Her son Jack (Ameche) becomes a crusading lawyer. Another son, Dion (Power), is a ne'er-do-well gambler, who falls in love with dance hall singer Belle Fawcett (Faye).
Through some luck Dion gains insider info about where a rail line in the city will be built. He and Belle build a saloon there, much to the disapproval of Dion's straight-laced mother. Dion builds an empire based on bribery and corruption in business and politics in direct competition with Gil Warren (Brian Donlevy), a similar crook. Gil offers to join forces with Dion if Dion will help him get elected mayor. Instead Dion backs his brother—which leads to conflict when Jack embarks on his crusade to clean up the city.
Then there's a big fire.
Jean Harlow was slated to star in this film before her untimely death from kidney failure. Her replacement Alice Faye became a big star. Power, Faye, and Ameche were teamed up again right after this in Alexander's Ragtime Band.
- Bar Brawl: Dance Hall Brawl, as Dion intentionally provokes an epic brawl at Warren's election-eve dance, in order to get all of Warren's political operatives arrested, so that Jack will get elected mayor.
- Be Careful What You Wish For: Dion gets his brother elected mayor. Jack then embarks on a campaign to clean up the Patch that is a direct threat to Dion's business interests.
- Bittersweet Ending: Jack is killed in the fire, but Dion and Belle are reconciled, and the movie ends with Mrs. O'Leary delivering a defiant speech about how a better Chicago will be built from the ashes.
- Blood from the Mouth: How we know Patrick is a goner after the horses break loose and drag him.
- The Chanteuse: Belle's job, singing on the stage, first in Warren's club and then in her own club.
- Distant Prologue: We see Patrick killed in 1854, then the rest of the story unfolds 1867-71.
- Downer Beginning: Patrick O'Leary is killed when his horses break loose from the wagon, just as they're on the outskirts of Chicago where he hopes to make a home for the family.
- Of Corsets Sexy: Belle wears a sexy corset while singing on the stage...
- Of Corset Hurts: ...but she doesn't like it and gasps with relief when she's pried out of it by her maid.
- Samus Is a Girl: Dion is surprised to find that the "B. Fawcett" whose name is on the map is the gorgeous Belle Fawcett.
- Spousal Privilege: After the final open break between Jack and Dion, Jack issues a subpoena to Belle. Dion then reforms, saying he'll help Jack clean up the Patch, and asks Belle to marry him. Jack performs the ceremony, and as soon as he pronounces Dion and Belle man and wife, Dion starts laughing. It was all an act designed to make sure Belle can't testify against him.
- Title Drop: "In Old Chicago" is one of the songs that Belle sings.
- Very Loosely Based on a True Story: Yes, there was a Mrs. O'Leary, and yes, the fire appears to have started in or near her barn. But her name was Catherine, she had a son and a daughter rather than three sons, and the character of Jack the lawyer is wholly fictitious. She did have a son named Jack who was a gambler and saloon owner, corresponding to the character of Dion. (And for that matter, no one is sure quite how the fire got started.)
- Whammy Bid: The auction for a charitable performance from Belle starts at $5 and goes up to $6. Dion then bids $100, an absurd amount in 1867, and wins.