from "Crime Pays: The Hollywood Gangster, 1930-1938" http://xroads.virginia.edu/~UG02/gangsters/publicenemy.html
Public Enemy - Plot Synopis
The plot focuses on the Powers family and how it is torn apart by the mob. The movie begins with a disclaimer from Warner Brothers: "It is the ambition of the authors of 'The Public Enemy' to honestly depict an environment that exists today in a certain strata of American life, rather than glorify the hoodlum or the criminal. While the story of 'The Public Enemy' is essentially a true story, all names and characters appearing herein, are purely fictional." This dissolves into another placard which reads 1909 and the scene then shifts to pre-prohibition Chicago where a young Tom Powers (Frank Coghlan when young, James Cagney otherwise) and his best friend Matt Doyle (Frankie Darro when young, Edward Woods otherwise) are drinking beer they have taken from a bar. The Audience is then shown the two boys stealing. Tom gives a stolen pair of skates to Matt's sister, which is discovered by his older brother, Mark who chastises Tom, setting the tone for their strained relationship throughout the movie. Tom's father, a police officer, finds out about the skates, and whips Tom. The audience is given the impression that this is common occurrence. Afterwards, Tom steals some watches and goes to his mentor, Putty Nose who is paying Tom and Matt for the stolen goods. He beguiles then with compliments while making a profit off of them.
The movie then skips ahead to 1915 and they are older but still running the same small time gigs. Mike has a respectable job and goes to night school. Tom and Mike are still at odds with each other, and Tom rarely comes home. Putty nose offers the boys a piece of a big job he's about to pull. They gladly accept, but during the robbery a shaky Tom shoots at an animal head hung on a wall, attracting the police. One member is of the gang is killed, and Tom and Mike run back to Putty Nose, who they learn has skipped town. They vow revenge.
1917, and WWI influences Mike to enlist. Tom goes upstairs to say goodbye to Mike, and Mike chastises Tom about his illegal escapades. Tom replies that Mike is embezzling small amounts from his company, and that he is not clean either. Mike hits Tom, knocking his younger brother to the floor. The only person Tom takes anything from during the entire movie is his brother Mike, and the only time Mike is violent is towards his brother.
1920, and Tom and Matt are truck drivers, and pull jobs for "Patty" Ryan who is an honest gangster, if such a thing is possible. Prohibition has just gone into effect and Patty discusses the lucrative opportunity in illegal liquor sales. They find a stash of liquor and rob it, successfully. Their success attracts others and "Nails" Nathan offers them "employment" as thugs to keep his buyers buying his beer. They are getting richer all the time and buy a new car and a wide selection of suits. They go to a club in their new getup, and hit it off with two girls.
Time passes and Mike returns form WWI wounded. At the welcome home dinner with Matt and his sister, Tom and Matt bring in a keg of beer. But Mike, who has learned of Tom's continued illegal activity, refuses to drink it, and tosses the keg against the wall calling his brother a killer. Tom retorts that his brother was also a killer in the war, and Mike collapses back into his chair. Tom and Matt depart and go back to the apartment they share with the two girls. The next morning a still angry Tom get a call from nails about a job and mentions his dissatisfaction with his woman over the phone, while she sits a few feet away. Sitting down to breakfast he asks her if she has any beer, and is angered when she says no. She asks his if he's found someone he likes more, and in the most famous scene from the movie, one that sums up the brutal man that Tom has become, Cagney snarls and smashes a grapefruit into her face.
Driving down the street Tom finds a new girl, Gwen (Jean Harlow) and drives her home. Later, that week at Matt engagement party to the girl he met back at the nightclub, Tom escorts Gwen. At the same party the two see Putty Nose, and when they leave that night they ambush him. Matt wavers as Putty pleads for his life but Tom shoots Putty in the head. Afterwards Tom goes home and gives his mother money, but Mike walks in and they fight. Mike kits Tom again, and Tom rips up the money.
He retreats to Gwens apartment where it is learned that she is holding out on him. He breaks up with her, but she tells him why she finds him attractive and they kiss. Just they fall onto the couch, Matt bursts in to tell Tom that Nails has been killed, by a horse. Tom leaves Gwen, forever, and in anger she shatters a wine bottle on the fireplace. Nails is buried but the gang breaks out into warfare without him. Patty hides them out, but Tom gets angry and leaves, Matt follows him and is shot by snipers. Tom gets away and ambushes the gang that killed Matt, shooting them all at a banquet where he is badly wounded. He falls into the gutter muttering that he's not as tough as he thought. In the hospital his brother makes up with him and his mother tells him how much she loves him.
He is then kidnapped by the rival gang, and in the final scene the Powers family receives a phone call that he is being returned. Ma goes upstairs to ready the room, when mike hears the knock. When he opens the door, a very dead Tom crashes to the floor. The last thing seen is another disclaimer, "The END of Tom Powers is the end of every hoodlum. 'The Public Enemy' is, not a man, nor is it a character -- it is a problem that sooner or later WE, the public, must solve."