Partially recovered from his fever, and reading the Book of Revelations, Freder is interrupted by and reunited with Josaphat, who explains how he evaded the Master's spy, the Thin Man: "I put on this disguise to escape from the Thin Man. But for ten days, your father's spy has been making even the workers' city risky..." Josaphat relates to Freder more of the strange events after his collapse: "On the evening you fell sick..." - and the film returns to the scene at Yoshiwara's where the false Maria performs a sexy dance. "...once the best of friends...because of that woman...the other man...the same evening...The Eternal Gardens lie abandoned, but night after night in Yoshiwara." The false Maria's dancing incites men, lured to her treachery and seductiveness at Yoshiwara's, to become mad, angry and aggressive toward each other. Freder cannot believe what he hears, that Maria is having a negative effect on the city: "And this woman, at whose feet all sins are heaped is also named Maria." Freder asks: "The same woman who those in the depths look up to as a saint --?!" Freder reminds Josaphat: "Many now go to the city of the dead, to a woman who has proven herself as true as gold...But the mediator must appear!"

The Thin Man reports to Fredersen in his office: "Only their hope for a mediator is keeping the workers in check." "Whatever happens tonight," Fredersen instructs the Thin Man in his office, "it is my express order to let the workers do as they will..." Meanwhile, Rotwang holds the real Maria captive, telling her about Fredersen's ultimate plan to stir up rebellion among the workers, to have them abandon their machines, and then quell the workers with brutal force:

Joh Fredersen wants to let those in the depths use force and do wrong, so that he can claim the right to use force against them....When you spoke to your poor brothers, you spoke of peace, Maria...Today, a mouthpiece of Joh Fredersen is inciting them to rebel against him...

Maria is devastated by news of the false Maria: "She will destroy their belief in a mediator!" But then Rotwang informs her of his own double-cross: "...but I have tricked Joh Fredersen! Your double does not obey his will - only mine!" In the attic with Maria, Rotwang grows ever more intoxicated by his triumph over Fredersen: "And I tricked Fredersen twice over -! For I concealed from him that his son wants to be your brothers' mediator - and loves you -!" But Maria is not the only one listening to Rotwang. Outside the attic window, Joh Fredersen has been eavesdropping.

At the same time, on the altar in the catacombs, the false, fanatical and beserk robotic Maria preaches a new message of protest and violent revolt to entice and prod the working class to rebel:

You know that I have always spoken of peace...but your mediator has not come...You have waited long enough! Your time has come -! Who is the living food for the machines in Metropolis -!? Who lubricates the machine joints with their own blood -?! Who feeds the machines with their own flesh --?! Let the machines starve, you fools- ! Let them die -!! Kill them - the machines -!!

Freder and Josaphat proceed down into the catacombs where they find the false Maria preaching dissension, and aghast, Freder cries out twice: "You are not Maria -!!! YOU ARE NOT MARIA -! Maria speaks of peace, not killing -! This is not Maria -!!" One of the workers recognizes Freder, and denounces him as the Master's son -- "Kill him, the dog, in his white silken fur - !!!" With his bare fists, Freder bravely fights off an assault of the workers, resulting in one of them being accidentally stabbed. Another worker shouts out for them to abandon the underground workers' city: "Get your women, your sons, from the workers' city! Let no one stay behind! Death to the machines -!!!" After the workers march away en masse, as a ferocious, club-wielding mob, to destroy the machines in the Underground City, Josaphat and Freder attend to the wounded worker, who recognizes that Freder is truly "faithful after all" - before he expires.

Joh Fredersen breaks into Rotwang's attic. He battles with his old rival, overcoming him. Maria is free. She races to the city's town square where the workers and their families have assembled under the direction of the false Maria. She rallies them and urges them to follow her: "Women and men, let no one miss today -! Death to the machines -!!" She leads them to the elevators that take them to the machines. One woman declares there is total support for the worker revolution: "Not one man - or woman remained behind -!" - although the children have not been evacuated. After ripping through outer iron gates, the mob storms the M-Machine and rushes toward the Heart Machine, the power house of Metropolis. Grot closes the gate and tries to notify Fredersen. Using an advanced videophone-communications system, Joh Fredersen speaks with chief foreman Grot and learns of the impending crisis. He sternly orders: "Open the gates!" Grot warns Fredersen that if the Heart Machine is destroyed, it would shut down energy for the city: "If the Heart Machine is destroyed, the entire machine district will end up in ruins." Finally, Grot obeys Joh Fredersen's order and opens the gates. The workers race to the Heart Machine, and confront Grot who stands alone to defend the machine:

Have you gone mad - ?? If the Heart Machine is destroyed, the entire workers' city will be flooded -!!

But his warnings are ignored and he is overwhelmed. The false Maria causes the Heart Machine to overheat and short-circuit until it crumbles, causing the pumps to stop turning which then produces a cataclysmic flood (as she escapes). After running from Rotwang's home, the real Maria comes upon the workers' city where she witnesses the failure of the machines. Water ruptures through the street and begins to flood the Underground City - the workers' quarters. She sounds the alarm in the transit, town-square area of the city with the giant gong and gathers some of the worker children together there to rescue them from the rising waters. The children clamor for high ground with arms outstretched, to be evacuated to safety.

The exploding Heart Machine and M-Machine cause the lights of the city to extinguish, witnessed by Joh Fredersen who now sits in his darkened high-rise office. The Thin Man informs the shocked Fredersen: "Do you know that your son is among the workers?" He asks: "I must know! Where is my son?!!!" The Thin Man replies: "Tomorrow, thousands will ask in fury and desperation: Joh Fredersen, where is my son -!", but Fredersen refuses to listen.

Josaphat and Freder join the real Maria - Freder hugs and kisses her: "Yes -- you! You are Maria -!" and they help her lead the worker children out of danger from the waist-deep water - "To the air shafts - quickly! Quickly! The reservoirs have burst! The city is flooding - !" At the upper end of the shaft, a metal fence blocks the children's path. More and more children press forward. Panic threatens. Freder and Josaphat scale the outside of the stair railing and hurl themselves against the bars. Finally Freder and Josaphat succeed in breaking down the metal gate. Freder climbs back down to get Maria and the last of the children. When they have escaped imminent danger, Freder proposes: "We'll take the children to the Club of the Sons!" Maria notices that all of the lights are out, due to the destruction of the machines. Soon after, Maria leads the last of the children to safety in the Club of the Sons.

Grot finally gets the attention of the workers, who joyously and obliviously celebrate the machines' destruction by dancing in a large circle. He reprimands them for their senseless, irresponsible actions which brought about the destruction of their children:

Where are your children??! The city lies underwater, the shafts are completely flooded -!! Who told you to attack the machines, you idiots? Without them you'll all die!!"

They scream back an answer: "It's the witch's fault -!" He responds: "Find the witch, this is all her fault -! Strike her dead -!!" and leads them on a witch-hunt rampage to find "the witch."

Back at Yoshiwara's, the false Maria celebrates and dances with the tuxedoed men, urging them: "Let's all watch as the world goes to the devil!" The party-going revelers leave Yoshiwara's to witness the massive destruction outside. And Rotwang revives in his attic, after his earlier battle with Fredersen. In front of Hel's monument Rotwang decides: "Now I'm going to take you home, my Hel!"

As Maria finishes bringing the children to safe refuge, she is spotted by Grot and the mob, who believe that she misled them and tried to drown their children. Grot cries out: "The witch ! the witch -! There she is -! there she is -! Where are our children, you witch -??! Burn the witch. - To the stake with her!!!" Suspecting nothing, Maria tries to speak. But the mob roars and throws hammers at her. Maria is hit. Only at the last minute does she escape the mob's wrath. Pursued by the mob, Maria runs headlong into the revellers from Yoshiwara. Grot grabs the false Maria and orders: "To the stake with her -!" While laughing wickedly, she is dragged and hoisted onto a large pyre of wood, tied up to a column, and burned. In the confusion, Freder believes that his beloved real Maria is being sacrificed in the growing flames, and screams out in despair while held back by the crowd: "MARIA --!!!" As the flames leap upward and burn the flesh of the false Maria, her metallic robotic shape metamorphoses and dissolves into view.

During the witch-burning, Rotwang confronts the real Maria nearby. The now-insane scientist, fearing the mob will seek retribution against him, also believes she is: "Hel -! My Hel -!!" He chases her into the cathedral, where she hangs onto a swinging bell rope, sounding another alarm. When Freder realizes that the burning witch is the false robotic Maria, he looks up at the cathedral where he sees Rotwang pursuing the real Maria, and he rushes to come to her rescue. As they fight on the cathedral's rooftop, watched by the workers (and his horrified father) standing below, Josaphat tells Grot that the children are actually safe: "Your children...saved -- !!!" - the workers are overjoyed by the news. In a struggle on the cathedral's rooftop, Rotwang loses his balance, tumbles backwards and falls to his death. Maria is saved and vindicated.

Joh Fredersen is convinced to reconcile with the workers, after having seen his son battle against the evil Rotwang, and demonstrate his strong love for Maria. The workers march in disciplined formation to the front entrance of the cathedral, where the reformer Maria urges Freder to be the mediator between Grot (representing the workers), and his ruling father/Master Joh Fredersen. There is the promise of a new, more equal synergy between the rulers and the ruled:

Head and hands want to join together, but they don't have the heart to do it...Oh, mediator, show them the way to each other....

Freder joins the hand of Grot (representing Labor) and his father (representing Capital) - becoming the Mediator between the classes, united by the Heart in Love:

THE MEDIATOR BETWEEN HEAD AND HANDS MUST BE THE HEART!

THE END