As they drive by in their open roadster down Michigan Avenue, Tom finds a new girlfriend walking down the street. She is a flashy and glamorous but mysteriously cool blonde named Gwen Allen (Jean Harlow). She hesitates about entering his car and his offer of a ride: "I'm not accustomed to riding with, uh, strangers." Tom assures her: "We're not gonna be strangers." In the back seat, they share their first discussion:

Tom: From Chicago?
Gwen: Not exactly. I came from Texas.
Tom: Where ya livin'?
Gwen: The Congress Hotel.

After they drop her off at her destination, she asks for Tom's phone number. [Jean Harlow's other sensational film at the time, Howard Hughes' Hell's Angels (1930), was released only a few months earlier.]

In a celebration at a nightclub for Matt's marriage to Mamie, attended by natily-attired gang members, Tom escorts his new voluptuous girlfriend Gwen. Matt tells Mamie that Tom "ain't the marryin' kind." During the party, Tom spots his former, double-crossing crime guide "Putty Nose," and is goaded on by Nails to show his toughness: "He thinks you're soft." Matt and Tom excuse themselves "for a little job" and Tom pulls his pal away from Mamie so they can trail Putty Nose in the dark shadows to his apartment.

They offer their boyhood mentor, who taught them how to "cheat, steal, and kill," an ironic compliment:

Matt: If it hadn't been for you, we might have been on the level.
Tom: Sure, we might have been ding-dings on a streetcar.

Then, in a cold-hearted murder scene to settle the double-cross from the past, after Tom cruelly plays cat-and-mouse with his prey, Putty Nose pleads for his life: "I don't wanna die." On his knees, he begs for Matt to protect him: "I'll do anything for ya from now on. Ain't ya got a heart, Mattie boy? Don't you remember how I used to play for ya, and didn't I always stick up for ya? I ain't got this comin'. Please, Matt. Matt, don't let him. Don't. I ain't a bad fellow, really." Putty Nose attempts to bring back boyhood memories by moving to the piano and playing one of the songs they used to laugh at in the club. Offscreen, Tom sadistically murders Putty Nose at point-blank range with two shots at the keyboard, all the while with a big smile on his face. Mute from the side, Matt observes helplessly with a stunned look as Putty Nose's body is heard collapsing on discordant piano keys.

Later, in a visit to his mother in her kitchen, Tommy offers her a thick wad of bills, but she refuses: "Mike wouldn't like it." From behind, Mike appears, telling his brother to leave and never again to offer "blood money" to them:

Tom: Don't you like it? It's more than you can do.
Mike: We don't want your money. I'm takin' care of Ma.
Tom: On two bits a week?
Mike: I don't go to nightclubs and she don't drink champagne...Get an earful of this. You ain't welcome in this house...That money is blood money and we want no part of it.
Tom: Hidin' behind Ma's skirts as always.
Mike: Better than hidin' behind a machine gun.
Tom: You're too smart. I'm goin', Ma.
Mike: And don't forget your change.
Tom: Money don't mean nothin' to me.
Mike: No, I guess not. With no heart and no brains, it's all you've got. You'll need it. (Mike slugs his brother in the face. Tom doesn't hit back, but rips the money in two and tosses it in his face)

As icy-cool Gwen flamboyantly lounges in expensive clothes in her apartment at The Congress Hotel, Tom admits that he first thought she was "on the make" and "different" from the kind of girls he was used to. He proposes that since they are mis-matched romantically, and he feels destined to never have her, his frustration makes him announce his decision to leave her:

Tom: I could never figure you out.
Gwen: Now can you?
Tom: No. Well, I guess I ain't your kind. I think you'd better call it quits.
Gwen: Oh, don't be like that, Tommy. Of course I go for you, as you say. Maybe too much.
Tom: You know, uh, all my friends, uh, think that things are different between us than they are.
Gwen: Yeah?
Tom: They figure they know me pretty well, and uh, they don't think I go for a merry-go-round.
Gwen: Do you think I'm giving you a merry-go-round?
Tom: No...
Gwen: Do you want things to be different to please your boyfriends?
Tom: No, but how long can a guy hold out? I could go screwy. (He rises to leave)

In a steamy, seductive love scene, to the tune of I Surrender Dear on the radio, Gwen mothers him and tells him why she is attracted to him:

Gwen: Where are you going?
Tom: I wanna blow.
Gwen: You're a spoiled boy, Tommy. You want things and you're not content until you get them. Well, maybe I'm spoiled too. Maybe I feel that way, too. But you're not running away from me. Come here. (She points and orders him to sit on her chaise. She removes his hat, tosses it away, and then sits on his lap) Now, you stay put, if you know what that means. Oh, my bashful boy. (Mothering him, she holds him to her breast) You are different, Tommy, very different. And I've discovered it isn't only a difference in manner and outward appearances, it's a difference in basic character. The men I know, and I've known dozens of them, oh, they're so nice, so polished, so considerate. Most women like that type. I guess they're afraid of the other kind. I thought I was, too. But you're so strong. You don't give. You take. Oh, Tommy, I could love you to death. (She kisses him and they fall into each other's arms)

Tom is interrupted, at this significant point in his life, by Matt's intrusion at the door. He is informed that "Nails" Nathan has been accidentally thrown by his horse in the park and killed - his head kicked in. Tom immediately leaves Gwen standing poised at the door - forever. She slowly walks back into the room and shatters a glass in the fireplace.

Headlines in the newspaper announce the gangland funeral for Nathan:

In a chilling scene following the funeral, a tux-attired Tom buys the spirited horse Rajah (the "bad animal - terrible, terrible," according to the stable man) for its value of $1,000 and then heartlessly executes the horse dead in its stall, to avenge the fatal fall of their beloved boss. The savage act is heard off-screen.

Gang warfares heat up - "the death of 'Nails' Nathan is said to have weakened the mob headed by Paddy Ryan." The headlines describe the brewing trouble:

Patrick J. Ryan's Bar is bombed by a rival gangster roadster that passes by, and the brewery is torched. Although Paddy believes: "They've got us on the run," Tom barks: "Not me. I ain't runnin'. I ain't yella." Paddy orders all the gang members to go into hiding: "I'm gonna need you. And you won't be no good to me when you're in the cemetery. Now I've got to have a couple of days to get the boys lined up again. When I'm done with that, you're gonna be where nobody knows to find ya except me."

In their new hideout where they are forced to remain, Paddy confiscates all their guns and money: "Come on, shower down...This won't be for long, boys. I'll have the mob lined up again in a couple of days." They are to be kept "comfortable" (with drinks and food) by an aging whore named Jane (Mia Marvin). An ominous camera angle captures an underneath shot of Paddy's car leaving the hideaway. An informant reveals their location to a rival gang by telephone. Later that evening, Tom peers through an illuminated opening in a black curtain, viewing a noisy coal delivery outdoors (sounding like machine-gun fire). Schemer's thugs set up a machine gun ambush nest in a second-story window directly across the street.

In a groggy, drunken stupor, Tommy is seduced by Jane when she puts him to bed. As she loosens his clothes, she cooes at him and pampers him in a motherly fashion:

Jane: You don't need to feel ashamed in front of me, Tommy. Here, let me help you.
Tom: I don't need any help.
Jane: Be a good boy and sit down. I'll take your shoes off, too. I want to do things for you, Tommy. You don't think I'm old, do you, Tommy? (while craddling his chin in her hand)
Tom: No.
Jane: You like me, don't you, Tommy?
Tom: Sure. (She kisses him) What's the idea?
Jane: Just a goodnight kiss for a fine boy.

The next morning at breakfast while serving him black coffee, Jane alludes to her seduction of him the previous night:

Jane: You aren't sorry, are you?
Tom: Sorry? Sorry for what?
Jane: For last night?
Tom: Whaddya mean? For gettin' drunk?
Jane: Aren't you the little play actor?
Tom: Wait a minute. Do you mean that...(She hushes his lips) Why you!

Disgusted with her deceitfulness, he hatefully slaps her, and then marches out of the apartment to go home, thereby defying Paddy's orders. He tells Matt: "I don't care what Paddy said. I'm gettin' out of this dump!" As they both leave the building, the coal delivery noise startles them while the machine-gun from across the street traces their steps, from the rival gang's point of view. When they get to the edge of the building, long-time partner Matt - who has followed Tom into the street - is viciously gunned down.

Foreshadowing his own death and with time running out, Tommy seeks to avenge his friend's death. He robs two .38 calibre pistols from a pawnshop and marches heavily armed to the Western Chemical Company, the headquarters of the rival Schemer Burns gang. Standing in the pouring rain on a rain-swept street, he watches the gangsters assembling inside.

In a horrific, climactic shoot-out scene in which Tom slaughters and eliminates his rival gang, the camera remains on the outside of the building as a barrage of shots and moaning screams of the wounded and dying are heard from inside. He single-handedly (but suicidally) manages to kill or seriously wound most of his enemy rivals, but he is also shot and wounded. He emerges from the building, stumbling, and then falling face down in a rain gutter on the torrential rain-soaked street. [The bizarre scene oddly prefigures Gene Kelly's joyous Singin' in the Rain (1952) number.] He tosses his two guns through the building's windows. From a low-camera angle, he again reels into the gutter, coughing and bleeding from a head wound. He utters an epitaph-like set of memorable words and ends up in a drain:

I ain't so tough.

After taken to an emergency hospital to recover, Tom is immobile, and bandaged from head to toe on a hospital bed. There, he is reconciled with his brother and mother. He apologizes to Mike and makes peace with him to renew their friendship: "Just sorry, you know." His mother clasps his hand - "so happy" that Tom is penitent - a lost child that will bring the family together again: "You're my baby." Affectionately, he gives her a soft fist tap to her chin. He promises her that he will come home - to stay: "Sure, coming home. If I can ever get out of here." Ma Powers is happy once more that he has apparently decided to go straight: "Both my boys back, all of us together again. I'm almost glad this happened." [Tommy's 'mamma's-boy' complex is more evident in Cagney's later gangster film, White Heat (1949).]

Paddy reports to Mike that Tom was helplessly kidnapped by his rivals from the hospital, and then resolves: "I'll bring Tom back if it's the last thing I do...I sent word to Burns that if he'd bring Tom back here tonight, I'd, I'd quit the racket. He could have it all. I'd leave town and I won't come back...It's a sweet offer."

The song, I'm Forever Blowing Bubbles, plays on the Victrola phonograph when a phone call to the Powers home reports that Tommy is coming home. His mother cheerfully goes upstairs and hums to herself as she prepares his room for his home-coming: "Oh, it's wonderful. I'll get his room ready. I knew my baby would come home."

In the rival gang's gruesome plan, Tommy's bullet-ridden, rope- and blanket-wrapped 'mummified' corpse/body is gift-delivered by a knock on the door. When Mike answers the front door, Tommy appears alive, bound from head to foot except for his exposed, bandaged and bloody face. It is the film's final memorable bone-chilling image - he tetter-totters on the doorstep, and then his mummy-body falls and crashes with a dull thud - face-first onto the floor. The needle on the revolving phonograph record becomes stuck, sounding like a heart-beat.

Mike examines the body of his brother - and then stares into the camera. Filmed from ground level and from the waist-down, he slowly and steadily walks toward the stairs in the interior of the house, presumably to tell Ma. The needle reaches the end of the record. The film's somber message appears over the image:

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.