Tony Camonte (Paul Muni), a gangster in Chicago, works as a bodyguard for crime lord Big Louis Costillo until being contracted by his buddy Johnny Lovo (Osgood Perkins) to kill Costillo. Though the cops bring Tony in for questioning, he quickly walks free, and Johnny takes over Costillo’s former territory on the South Side. Tony becomes his second-in-command.
Now that he’s gotten a taste of a bigger salary and more power, Tony is eager to expand the empire even farther, into the North Side. This is a bridge too far for Johnny, who pleads with Tony to leave the North Side in the control of Irish gangster O’Hara.
That doesn’t deter Tony in the least. He’s confident his gang will someday take over the North Side and dethrone O’Hara’s gang. Not only that, he believes he’ll succeed Johnny as the head honcho, and starts getting flirtatious with Johnny’s girlfriend Poppy (Karen Morley).
Because Prohibition has just come in, Tony also wants to increase their crime empire and earn more easy money through bootlegging. Johnny is also keen to do this, but insists on waiting until after Costillo’s funeral to discuss the matter.
We then meet Tony’s kid sister Francesca (Cesca) (Ann Dvorak). He’s furious to discover she’s in the entry hallway kissing some guy instead of eating dinner at home. After Tony chases away her date, he insists he doesn’t want any men touching her, and gives her money to have fun without guys.
Mrs. Camonte (Inez Palange) highly disapproves of her accepting dirty money, but Cesca is determined to live her own life as she sees fit.
Johnny takes over Costillo’s former club without any difficulty, and his gang’s control over the South Side increases even more. Tony and some of his buddies set up a bootlegging operation and begin overselling their beer to every local speakeasy. They also start putting out a lot of hits on rivals and people standing in their way.
One of these shootouts is at The Shamrock, run by O’Hara’s gang. With their rival’s top men permanently out of the picture, it seems as though the North Side is theirs. There’s a little snag when the newspaper reports one of the gangsters survived and is in hospital, so Tony and his guys pay him a little visit to take care of this problem.
Tony tries to put the moves on Poppy again, but she refuses his advances, despite feeling some attraction to him. Johnny is also angry to learn he put out a hit on the North Side, since O’Hara will now be out for blood. As they’re all arguing, a car speeds down the street and throws out a dead body, with a note pinned to him:
STAY OUT OF THE NORTH SIDE
Soon afterwards, Poppy calls Tony multiple times to arrange a meeting. The message doesn’t get through the first time on account of Tony’s dimwitted secretary Angelo (Vince Barnett), a great bit of comic relief. Finally, Tony answers the phone himself, and to his great delight learns Poppy is right outside.
Poppy brings the news that O’Hara was taken out that morning in a flower shop, which explains why a fellow gangster just brought a carnation. While she and Tony are getting friendly in his place upstairs, the cops appear outside. Tony sends her to safety down the stairs through a back door and arranges a date that night.
Enter rival crime lord Tom Gaffney (Boris Karloff), who’s just received a fine shipment of sub-machine guns. When he’s tipped off that he’s being trailed, he figures out a way to get his precious new weapons to safety.
Tony has gotten out of legal trouble the same way he did earlier, by having his lawyer cite habeas corpus to the cops. With that matter easily settled, he goes to meet Poppy at the restaurant.
Alas, their date is interrupted by a big shootout. Angelo once against provides great comic relief by being completely unharmed as he talks on the phone right in the middle of the violence.
Tony is thrilled to discover an abandoned machine gun, particularly since it’s portable. This isn’t the kind of machine gun you have to operate in a stationary position. You can take it on the go with you.
Tony demonstrates the use of this magical weapon to Johnny, whom he has another fight with, and starts putting out hits on North Side rivals.
The violence continues fast and furious, leading cops to beg a newspaper editor to quit glorifying gangsters or even giving them any coverage at all. The editor says he can’t change anything unless the laws change first. That’s politicians’ responsibility, not his.
Tony is shocked and angry to see Cesca wearing a sexy dress and dancing with his buddy Guino “Little Boy” Rinaldo (George Raft) at a nightclub. This completely distracts him from his and Johnny’s rivalry for Poppy’s attentions, and he drags Cesca home, breaks a strap of her dress, and hits her. Once again, he insists no man can ever have her.
Then the power struggle between Tony and Johnny starts intensifying, with the stakes increasingly higher. Even more trouble appears when Tony returns from a month-long Florida vacation with Poppy and learns Cesca moved out. Tony storms over to her new home and flips out to see Guino is living with her.
Now the stage is set for one final confrontation between Tony and the law, with the highest stakes ever.
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