Stewart "Stew" Smith (Robert Williams), ace reporter for the Post, is assigned to get the story about the latest escapade of playboy Michael Schuyler (Donald Dillaway), a breach of promise suit by chorus girl Gloria Golden, who has been paid to drop it. Unlike rival Daily Tribune reporter Bingy Baker (Walter Catlett), he turns down a $50 bribe from Dexter Grayson (Reginald Owen), the Schuylers' lawyer, to not write anything. He does pretend to be swayed by the pleas of Anne (Jean Harlow), Michael's sister, but then brazenly calls his editor with the scoop, appalling the Schuylers.
Stew returns to the house to return a copy of Conrad he had taken from the Schuylers' library. The butler, Smythe (Halliwell Hobbes), tries to make him leave, but Anne sees him. Stew surprises Anne by presenting her with Michael's love letters to Gloria, who had intended to use them to extort more money from the Schuylers. Anne offers Stew a $5,000 check, which he refuses. She asks why he reported the suit, but not the love notes. Stew explains that one was news, the other, blackmail. He later tells her he is writing a play. Intrigued, Anne wonders if she can turn him into a gentleman. She invites him to a party at the house.
They fall in love and soon elope, horrifying Anne's widowed mother, Mrs. Schuyler (Louise Closser Hale), an imperious dowager who looks down on Stew's lower-class background. Michael takes it in stride, telling Stew he's not as bad as everyone thinks. The wedding is scooped by the rival Daily Tribune, enraging his editor, Conroy (Edmund Breese). Even more upset is Stew's best friend Gallagher (Loretta Young), a "sob sister" columnist secretly pining for him. Conroy taunts Stew as "a bird in a gilded cage." Despite his bravado, Stew is upset by the implication he is no longer his own man, vowing not to live on Anne's money. However, she cajoles him into moving into the mansion and starts to make him over, buying him garters (despite his objections) and hiring a valet, Dawson (Claud Allister).
When the Schuylers hold a reception for the Spanish ambassador, Gallagher substitutes for the society reporter and chats with Stew. Anne is surprised to learn that her husband's best friend (whom she had assumed was a man) is actually a lovely young woman and treats Gallagher icily. Then, Bingy tells Stew the Tribune will give him a column if he signs it "Anne Schuyler's husband." Insulted, Stew punches Bingy when he calls him Cinderella Man. The next morning, Mrs. Schuyler is aghast to find Stew's brawl has made the front page.
Wrestling with his play, Stew invites Gallagher and another friend, Hank (Eddy Chandler) from Joe's. They arrive with Joe and several bar patrons in tow and even Bingy shows up to apologize. A raucous party ensues. Meanwhile, Stew and Gallagher ponder the play, deciding to base it on Stew's marriage. Anne, Mrs. Schuyler, and Grayson return as the party is in full swing. Stew apologizes for letting the party get out of control, but protests that he can invite friends to "my house." Anne replies, "Your house?"
Stew returns with Gallagher to his own apartment. Along the way, he gives a homeless man his expensive garters. Grayson stops by to say Anne will pay him alimony, whereupon Stew punches him (earlier, Stew had warned Grayson that his twentieth insult would earn him a "sock to the nose"). Stew tells Gallagher the play could end with the protagonist divorcing his rich wife and marrying the woman whom he had always loved without ever realizing it. Overwhelmed, Gallagher hugs him.

Question: Why does Stew punch Bingy?
Answer: He calls Stew Cinderella Man.
Alternative answer: Bingy called him a "Cinderella Man".