The rest of the Cohan family are on the road, stranded in the waiting room of a Midwestern Illinois railroad station during a rainstorm. They read about Georgie's success in New York in a newspaper, where he is billed as "the new Broadway sensation." Jerry reacts with a slight bit of jealousy, although he won't admit it: "But it ain't right. We've got a good act and we've built our own reputation. We'd be billed as we should be billed - the three Cohans...Listen, don't think I'm jealous of Georgie's success, even though I am a better actor." Another actor in the room puts things in perspective:

Still, it does look a little funny. George being the toast of Broadway and you folks gathering a few crumbs in the tank towns.

But then, the Cohans are summoned by the ticketmaster, who presents them with a telegram. They are invited back to New York to be reunited again with George on Broadway - "the four of us back together again - and on Broadway!":

Telegram: Impossible to find three clever actors named Cohan for my new show anywhere in New York. Return immediately for rehearsals.

A montage of billboard signs, a common transitional element in the film, advertises a series of their performances as The Four Cohans. Back together, the four are dancing and singing on stage:

• THE FOUR COHANS in their sensational coterie of comedy, songs, and dancing at the Lyric Theatre
  (Oh, You Wonderful Girl)
• THE FOUR COHANS, now appearing at The Majestic Theatre
  (I'll Be True to You)
• Opera House, Now Playing, THE FOUR COHANS, a mirthful melange of scintillating songs and dances
  (The Barber's Ball, performed in clown costumes)

In a dissolve to Mary's apartment, George is playing the piano and has just finished writing a tribute song to her (to his "one particular, very special Mary") - one that she will sing in his new forthcoming show (and it's "the best song in the show"). He speaks the lyrics as she accompanies him on the piano the first time through, and then she sings the song afterwards:

Mary

My mother's name was Mary. She was so good and true.
Because her name was Mary, She called me Mary, too.
She wasn't gay or airy, But plain as she could be.
I'd hate to meet a Mar-y, Who called herself Ma-ry.
For it is Mar-y, Mar-y, Plain as any name can be.
But with propriety, Society will say Ma-ry!
But it was Mar-y! Mar-y! Long before the fashions came.
And there is something there, That sounds so square,
It's a grand old name.

With her heart aglow with warmth, Mary is reassured that the song will always be associated with her and with their love:

Mary: Gee, you never cared much for my name before. It was kinda common. Gee, there's millions of Mary's around. Now...
George: I didn't write it for the millions of Mary's. I wrote it for one particular, very special Mary.
Mary: It's a wonderful feeling having your name written in music.
George: And not bad music either, huh?
Mary: Nope, it isn't. But how will everybody know that I'm 'the Mary'? I wanna make sure that everybody knows it was written for me.
George: They'll know all right. When they look at you singing that song and then look at me looking at you, they'll know.

At that very moment, Sam Harris barges in - he is anxious to take George to the Lyceum to meet famous Broadway star Fay Templeton and lure her to become the "leading lady" in their new show. [Real-life star Templeton appeared in only one film in her career, Broadway to Hollywood (1933).] At the downtown Broadway theatre, a huge, lighted marquee reads: "KLAW & ERLANGER present FAY TEMPLETON in A Little Bit of Everything, 2nd Big Year, Last Week." Worried that George will be too crude and forward with the star, Sam advises George as they arrive: "You don't tackle a star like Miss Templeton. You approach her, and very tactfully too."

Beautiful Fay Templeton (Irene Manning) is in her upstairs, well-furnished dressing room, where promoter Abe Erlanger (George Barbier) is encouraging her to 'listen' to George who purportedly has the "golden touch." But the glamorous, self-important, dignified star resists:

One hit! He may be a flash in the pan, for all we know. And I heard about Little Johnny Jones. And I read the critics. Of all the loud, vulgar, flag-waving...What I want is a quiet, dignified, musical play. I want to perform in a theater, not a boiler factory.

George makes a flat joke when asked if he can write a play without a flag: "I can write a play without anything except a pencil." She cuts him off, definitely uninterested in the brash, tactless manner in which George operates: "I'm afraid I would never please the sort of people who revel in your antics and fireworks." And in her "exit speech," she doesn't wish to discuss things any further after her show's performance:

After the show, I'm going home to New Rochelle. It's only 45 minutes from here, but thank heavens it's like a thousand miles from all the noisy, neurotic people one has to associate with in our profession.

Sam sarcastically compliments George for his "wonderful tact" with the star. After the first act, Fay hasn't changed her mind and won't even consider Erlanger's persistent testimonial praise for the young rising composer's talent, and his advice for her to 'hitch' her wagon 'to his star':

Erlanger: He's the most original thing that ever hit Broadway. And do you know why? Because he's the whole darn country squeezed into one pair of pants. His writing, his songs, why even his walk and his talk. They all touch something way down here in people (He gestures to his heart.) Don't ask me why it is, but it happens every time the curtain goes up. It's pure magic.
Fay: I'm bored by magic. I know his formula. A fresh young sprout gets rich between 8:30 and 11:00 pm.
Erlanger: Yes, that's just it, Fay. George M. Cohan has invented the success story. And every American loves it because it happens to be his own private dream. He's found the mainspring in the Yankee clock - ambition, pride, and patriotism. That's why they call him the Yankee Doodle Boy. Now, if you'll take a tip from me, Fay, you'll do just what I'm doing. You'll hitch your wagon to his star right now.

When she returns to her dressing room after the first act of the show, George has been working feverishly at the piano. He presents her with a song "dedicated" to her - he was inspired to write 45 Minutes From Broadway just for her in the short stretch of time while she was onstage during the first act. Her exit speech to him struck him as the "perfect title for a show and a perfect title for a song." She regards him as persistent, so she lets him audition his song for her while she changes her costuming:

45 Minutes From Broadway

Only 45 minutes from Broadway, Think of the changes it brings,
For the short time it takes, What a diff'rence it makes
In the ways of the people and things.
Oh! What a fine bunch of rubens, Oh, what a jay atmosphere,
They have whiskers like hay, And imagine Broadway,
Only 45 minutes from here.

Enthusiastic that Ms. Templeton is being swayed to join their production, Sam hastily volunteers George's other song Mary ("the best thing he's ever done") to Fay - without George's approval. As Sam grabs and hands the sheet music for Mary over the dressing room curtain to her, Cagney vehemently protests: "That's not for her. She doesn't sing that" - and he downplays it as only a "so-so number," but Fay is nonetheless interested. The scene cuts from Fay sitting down at the piano and humming the tune in the dressing room to a parallel scene - Mary is singing and playing the song on her piano in her apartment.

Through the hallway door outside Mary's apartment, where George arrives with a huge bouquet of flowers and a box of candy to soften the blow of giving away her song in exchange for Fay Templeton's participation as 'leading lady', he is afraid to break the news to Mary when he hears her playing his song on the piano. After he greets Mary, he changes the subject - to the food he smells for dinner:

George: Hmm, ham or bacon.
Mary: Bacon.
George: Good, ham makes me self-conscious.

To his surprise, she has already decided that Fay Templeton should be in his show:

I think you ought to give in to her...no matter what she asks...Oh, I don't care for Templeton. I'm looking out for you. Think what it means for you to have a star like Templeton in your show.

Selflessly, Mary rarely thinks about herself and has already guessed that his lavish gifts meant that he had given her song away. She settles on being a 'looker-after' for him, and accepts his marital proposal to make her his life-long "leading lady." [Cohan's two marriages were to wives named Ethel and Agnes.] He offers her marriage with show-business metaphors - in the affecting, romantically-emotional scene:

George: Always worried about me, aren't ya? Ever think about yourself?
Mary: Not much lately. Haven't had time. The minute I saw you without your beard, I knew here was a little boy who needed a lot of looking after. So I gave myself the job. There are a lot of singers, you know (she winks at him), but very few really good looker-afters.
George: Darling, how would you like a lifetime job of looking-after? Leading lady - run of the play. There may be a few heartaches after the curtain goes up, but I can guarantee you some laughs. How does it sound?
Mary: I think I might like it, Mr. Cohan. Could I, uh, see some of the script? (He kisses her.)
George: Not bad for a first reading...(with dread) Oh darling, uh, there's something I forgot to tell you.
Mary: (softly) Yes, dear.
George: Uh, I gave your song to Fay Templeton tonight. (She smiles sweetly back at him.) Darling, did you hear me? I, uh, I gave your song to Fay Templeton tonight.
Mary: Yes, I know. I knew you did, dear, when you brought the candy and flowers. (George looks back with bewilderment.)

A white-gloved audience member (Mary) in a box seat opens her New Amsterdam Theatre (a Broadway theater) program to the frontispiece - "George M. Cohan's 45 Minutes From Broadway, starring Fay Templeton and Victor Moore." [Cohan's play was made into the silent film 45 Minutes From Broadway (1920).] On-stage, Fay sings Mary, the opening number. The threesome of Sam, Mary, and George sit in the upper box seats during the performance:

Sam: That's a wonderful song, George - the best you've ever done. It'll live for years.
George: Thanks, Sam, but I still think Mary should have sung it.
Mary: Oh, that's all right. Fay has the song. I have the author. (She places her wedding-ringed hand on George's hand.)

The chorus sings 45 Minutes From Broadway with a stage backdrop of the New Rochelle railroad station. Fay (playing the role of Mary), returns to sing So Long, Mary as she departs on the train.

Cohan's next Broadway success is George Washington Jr., that stars George with his "Royal Family." Eddie Foy (Eddie Foy, Jr. playing his vaudeville-star father) and George, two of the biggest names on Broadway, meet anonymously on the street outside the theatre, where they exchange one-liners, quips and jibes about each other's work. George impersonates Foy's lisp and habit of talking with one hand over his mouth. [The two did meet in late 1907, although their encounter was undoubtedly different from this one. They reportedly despised each other.] Foy is reading the poster outloud to himself outside the theater when George appears:

Foy: ...He certainly did give himself a billing, this George M. Cohan.
George: You don't have to memorize that one, kid. There's plenty more all over town.
Foy: I'd like to forget it. Say, mister, you connected with this turkey?
George: What makes you think it's a turkey? I hear it's pretty good.
Foy: It's a malicious rumor to gyp the public. Who is this guy Cohan? Where's he from? What is he, an upstart?
George: Oh, he's been through the mill. Played everything. Small time, big time, vaudeville, rep shows. Even followed dog acts.
Foy: Must've looked like an encore. Say, uh, is he as good as Foy?
George: Who?
Foy: Foy, Foy. (Foy sprays George's face) Eddie Foy. Oh, pardon me.
George: Pardon me. I didn't quite catch the name. Would you mind spraying it again?
Foy: Eddie Foy! The star that's got the big show down the street with a chorus of seventy.
George: Why, I thought they looked a little younger than that. I hear now that Cohan's in town, Foy is gonna retire.
Foy: Foy won't retire till he's ninety!
George: Is it gonna take him that long to discover he has no talent? Why, they tell me when he tries to sing, the orchestra puts up umbrellas.
Foy: Tries to sing! Foy is a genius! He keeps his audience glued to the seats.
George: That's one way o' keeping them in the theater. Cohan does it with talent. Look (he points out the poster) - produces his own plays, writes his own books, lyrics and music, plays the leads, and he's a great dancer.
Foy: He dances, eh? When does he get time to practice?
George: When you write your own plays you don't have to practice. Cohan's done all right. He's given the world 'Yankee Doodle Dandy.' What's Foy done for his country?
Foy: He gave 'em seven kids.
George: Does he dance?
Foy: One o' the best.
George: When does he get time to practice?
Foy: Say, listen, young fella. My name's Eddie Foy.
George: I know it. I'm George M. Cohan.
Foy: Oh, so you're Cohan? (They shake hands) Well, if I said anything accidental to make you mad, I want you to know I'm darn glad I did.
George: I don't blame ya. I'd feel the same way if I were up against Cohan. What do you like to drink?
Foy: Oh, moxie-
George: I can supply it! The attraction inside is a whole lot bigger than I am. Come and see it when your show closes.

The show, with a cast of 260 people, begins with an elaborate musical number: You're a Grand Old Flag. Uniformed Yankee soldiers observe a flag-raising ceremony during the playing of taps. With the billowing flag as the centerpiece surrounded by Boy Scouts and the troops, George sings the tune with embedded excerpts from Dixie, Auld Lang Syne, The Battle Hymn of the Republic, When Johnny Comes Marching Home, My Country 'Tis of Thee, tableaus of Betsy Ross sewing the flag, a rag-tag Revolutionary War parade, slave-workers, the Lincoln Memorial and words from Lincoln's writings (The Gettysburg Address: "...and that government of the people, by the people, for the people shall not perish from the earth"), a Teddy Roosevelt look-alike leading the troops into the Spanish American War, and the mobilization of ordinary citizens during wartime. The patriotic, rousing number of democratic ideals includes the familiar chorus of the title song:

You're a Grand Old Flag

You're a high-flying flag
And forever in peace may you wave
You're the emblem of the land I love,
The home of the free and the brave!

Every heart beats true
'Neath the Red, White, and Blue,
Where there's never a boast or brag.
But should auld acquaintance be forgot
Keep your eye on that Grand Old Flag.

George tap-dances with flag-bearing, stars-and-stripes decorated chorus girls (Mary and Josie). Uncle Sam (Jerry) escorts a white-costumed 'Statue of Liberty' (Nellie) to center stage for the finale in front of the nation's Capitol.

In a series of overlapping dissolves, the show is taken on tour from city to city - it is a triumphant smash hit. More Cohan shows follow: "The Honeymooners," "The American Idea," "The Man Who Owns Broadway," and "Hello Broadway." As he leaves the backstage of a theater, George is besieged by autograph-seekers:

Autograph seeker: Can I have your autograph, Mr. Cohan?
Woman: To what do you attribute your continued success, Mr. Cohan?
George: Oh, I'm an ordinary guy who knows what ordinary guys like to see...(The scene quickly shifts to a Happy New Year celebration in 1912 to suggest the passage of time) Front row center! The greatest show on earth. The people!
Mary: (toasting) To the people, God bless them!

On the Cohan country farm, Nellie and Mary are feeding chickens out front, and George is chopping kindling wood with Josie in the back. George has purchased a silk smoking jacket for his father's birthday present, while Josie has bought him a beautiful gold watch. George is taken aback when he hears Josie's plan to marry Fred Niblo Jr. - a threat to the unity of the Cohans, but he warms up to her:

George: Little Josie's gonna get married, huh? It doesn't seem that long ago. What happens to the Four Cohans?
Josie: Oh, just a simple case of subtraction. You know, one from four leaves three - Three Cohans.
George: That's only arithmetic. One Cohan from Four Cohans - leaves nothing. Do Mom and Pop know?
Josie: (she nods) Mom's been working on the wedding dress for weeks. What are you thinking about, Georgie?
George: I'm gonna write you the most terrific wedding march ever put on paper. It'll pack the pews!

Before their father's surprise sixty-second birthday celebration (around 1915), George shows concern about the destructive effects of Josie's marriage on the sanctity of the performing Cohan family: "That's no reason to break up the act. The Four Cohans is just as much an institution as marriage is." It is inevitable, however, that the family will break up - his parents give their "two weeks notice" to retire to their farm: "George, I'm afraid your mother and I are breaking up the act before Josie is."

After opening up his birthday gifts, Jerry reads a letter that George has sent to him for the occasion - the first he has received from him "in twenty years." In their quiet company during an emotion-laden sequence, George bequeaths a half-interest in all of his theaters and plays to his father and mother:

Dead Dad: This is your sixty-second birthday and God bless you. Maybe I've never told you before but no son ever had a better dad or one to be prouder of - You and mother have always given me more love and understanding than I ever deserved, and all the luck I've had is due to the things you two have taught me. Nothing I can do could ever repay the debt - but here's a little present for you and mother. From this day on, you and I are partners in every theater and theatrical property I possess, half and equal. The Cohan theater, the Astor, the Gaiety, and the Grand Opera House in Chicago. And all my plays and songs as long as they or you and I live. (Tears well up in the eyes of his parents. Deeply affected by his son's generous gesture, Jerry has difficulty finishing the letter and he pauses with an off-hand comment about his inadequate reading glasses.)...Wish you all my love, your son and partner, George.

Nellie 'steals' the scene by bursting into tears.