 Infuriated at being told to write one final column after being laid off from her newspaper job, Ann Mitchell (Barbara Stanwyck) prints a letter from a fictional unemployed "John Doe" threatening suicide on Christmas Eve in protest of society's ills. When the letter causes a sensation among readers, and the paper's competition suspects a fraud and starts to investigate, editor Henry Connell (James Gleason) is persuaded to rehire Mitchell, who schemes to boost the newspaper's sales by exploiting the fictional John Doe. From a number of derelicts who show up at the paper claiming to have written the original letter, Mitchell and Connell hire John Willoughby (Gary Cooper), a former baseball player and tramp in need of money to repair his injured arm (by Bonesetter Brown), to play the role of John Doe. Mitchell starts to pen a series of articles in Doe's name, elaborating on the original letter's ideas of society's disregard for people in need.
Willoughby gets $50, a new suit of clothes, and a plush hotel suite with his tramp friend "The Colonel" (Walter Brennan), who launches into an extended diatribe against "the heelots", lots of heels who incessantly focus on getting money from others. Proposing to take Doe national via the radio, Mitchell is given $100 a week by the newspaper's publisher, D. B. Norton (Edward Arnold), to write radio speeches for Willoughby. Meanwhile, Willoughby is offered a $5,000 bribe from a rival newspaper to admit the whole thing was a publicity stunt, but ultimately turns it down and delivers the speech Mitchell has written for him instead. Afterward, feeling conflicted, he runs away, riding the rails with the Colonel until they reach Millsville. "John Doe" is recognized at a diner and brought to City Hall, where he's met by Bert Hanson (Regis Toomey), who explains how he was inspired by Doe's words to start a "John Doe club" with his neighbors.
The John Doe philosophy spreads across the country, developing into a broad grassroots movement whose simple slogan is, "Be a better neighbor". However, Norton secretly plans to channel support for Doe into support for his own national political ambitions. When a John Doe rally is scheduled, with John Doe clubs from throughout the country in attendance, Norton instructs Mitchell to write a speech for Willoughby in which he announces the foundation of a new political party and endorses Norton as its presidential candidate. On the night of the rally, Willoughby, who has come to believe in the John Doe philosophy himself, learns of Norton's treachery from a drunken Connell. He denounces Norton and tries to expose the plot at the rally, but Norton speaks first, exposing Doe as a fake and claiming to have been deceived, like everyone else, by the staff of the newspaper. Despondent at letting his now-angry followers down, Willoughby plans to commit suicide by jumping from the roof of the City Hall on Christmas Eve, as indicated in the original John Doe letter. Mitchell, who has fallen in love with Willoughby, desperately tries to talk him out of jumping (saying another John Doe has already died for the sake of humanity), and Hanson and his neighbors tell him of their plan to restart their John Doe club. Convinced not to kill himself, Willoughby leaves, carrying a fainted Mitchell in his arms, and Connell turns to Norton and says, "There you are, Norton! The people! Try and lick that!"
What does Willoughb eventually plan to do? What is Norton's underlying plan? What does Willoughby plan to do after being double crossed by D.B. Norton? Why does Ann Mitchell desperately try to talk Willoughby out of suicide? Why does Ann Mitchell print the John Doe letter in the newspaper? What was John Willoughby's previous career? What does Mitchell do to help sell John Doe to the newspaper audience? What happens after the letter is printed? What does Willoughby find out about John Doe in Millsville? How much was  Willoughby bribed for? What is the slogan of the grassroots movement inspired by the John Doe philosophy? What holiday does Willoughby's suicide attempt have in common with the original John Doe letter?  Who bribes Willoughby? What does Willoughby plan on doing after Doe is exposed as a fake? What was Ann Mitchell given $100 a week to do? What happens after Willoughby's first radio performance? What does the fictional character "John Doe" threaten to do? What did John Willoughby need money for? What secret ambition motivated D.B. Norton to carry on the John Doe ruse? What theme do the John Doe letters have in common? Who do Mitchell and Henry Connell hire to play Dear John? What slogan does the John Doe movement create? What is Mitchell paid $100 per week to do? What idea does Mitchell have after she's rehired? Who does Willoughby learn about Norton's plans from? What does Willoughby get for his troubles as portraying John Doe? What day does John Doe threaten to commit suicide? What was John Willoughby's former occupation? Why did Willoughby's plan to run away fail? Who has fallen in love with Willoughby and desperately convinces him not to jump?