A mighty syndicate of financiers wishes to exploit the untouched deposits of oil under the streets of Paris, and they ignore humanity, beauty, and truth in the process. The free souls of Paris oppose the men and eventually triumph by literally removing the syndicate from the scene.

On one side are the President, the Prospector, the Baron, the Press Agent, the Broker, and the Ladies of the Street. On the other side are the Waiter, the Little Man, the Street Singer, the Flower Girl, the Shoelace Peddler, the Ragpicker, and other folk. In the middle, and significantly devoted to the gentle souls, is the Madwoman of Chaillot, aided by her compatriots, the Madwomen of Passy, St. Sulpice, and La Concorde. The capitalistic forces function as well-oiled machinery; they are devoid of characteristics that set them apart or elicit for them the least bit of empathic reaction. The people of Paris are all recognizable types, but each possesses some quality of individuality.

The Madwoman encounters the President, the Baron, the Prospector, and the Broker at a sidewalk café in the Chaillot district. Her friends are all aware that something terrible is afoot and inform her of the plot to drill for oil beneath the streets. The Prospector sends his agent with a bomb to destroy the city architect, the only obstacle to the drilling. Pierre, the young assassin, is rescued by the Policeman as he is about to throw himself into the river rather than carry out his task. He is revived and convinced by the Madwoman that life is really worth living.

It is apparent to the Madwoman that the only way to combat the materialistic interests is to annihilate them. She and her friends have little chance of opposing them if commonly interpreted methods of justice are used, so she decides upon an infallible plan and sends her confederates scurrying about on errands to help her carry it out.

The Madwoman retires to her quarters in the rue de Chaillot to receive the delegation of capitalists. They answer her invitation because she has informed them that a large deposit of oil rests under her basement. To prove it, she prepares a sample; a bottle of mixed kerosene and mange cure is waiting for the Prospector, who professes to be able to detect the existence of oil deposits by merely sniffing the air.

Some years before, the Madwoman had rescued a Sewer Man who had promised to show her a secret entrance from her basement into the sewers of Paris. She summons him and he presses the stone concealing the entrance. The other Madwomen, Mme Constance, who takes her invisible lap dog with her everywhere; Mlle Gabrielle, who talks to nonexistent friends; and Mme Josephine, who is an expert at jurisprudence because her brother-in-law is a lawyer, all arrive for a delightful tea scene. They are mad, but that fact in no way prejudices the trial that follows.

Mme Josephine is called upon to conduct a court, for it is only just and proper that the financiers have a fair hearing before they are sent to oblivion. The Ragpicker agrees to speak in their defense, and a damning testimony it is, with money at the root of their materialistic evil. The verdict of the tribunal is unanimous; the accused are guilty on all charges. The Madwoman is authorized to proceed with the extermination.

The guests begin to arrive, and in a wonderful scene of comic irony each group in turn is sent through the door into the sewer. First comes the President, next the Prospector, then the Press Agent, and so on until all, like sheep, have followed the infallible nose of the Prospector down the dark stairway, never to return again.

Immediately, all the wrongs of the world are righted. The pigeons fly again; the air is pure; the sky is clear; grass sprouts on the pavements; complete strangers are shaking hands. Humanity has been saved, and the friends of friendship thank the Madwoman, the triumphant feminine force.