After receiving a tip that Hiroshi Sato was manufacturing Equalist weapons in a factory beneath his home, the Metalbending Police Force conducted a raid on the Sato estate and subsequently discovered the hidden factory.
Tenzin, Korra, Chief Beifong, and several metalbender officers arrived at the factory, leaving Mako, Bolin, and Asami waiting at the entrance under the supervision of Officer Song. Shortly after the others' departure, Mako and Bolin knocked out Officer Song and proceeded down toward the factory, as they were worried for the others' safety. However, a conflict ensued as the entire group had been confronted by Hiroshi Sato, the Lieutenant, and a number of other Equalists. During the battle, Hiroshi utilized the abilities of his mecha tanks for the first time. At this point, Chief Beifong realized that the tip they had received earlier was part of Hiroshi's plan to lure them into his underground factory. After defeating the invading force, Hiroshi ordered that they be taken to Amon. Asami subsequently arrived at the factory and confronted her father, who asked her to join him and the Equalists. Asami appeared willing to take the offer, accepting an electrified glove from her father, but instead used it to shock him and the Lieutenant, buying Tenzin, Lin, and Team Avatar, including herself, enough time to escape. The remaining members of the police force, however, were captured by the Equalists and brought before Amon to have their bending removed.
The factory is very large and is accessible via a minecart-like device that carries people deep into the mountainside. The factory has retractable walls made out of platinum - a metal so pure that metalbending has no effect on it. There are two large banners bearing Amon's face hanging from a metal beam in the factory.
- The posters in the underground Equalist factory read " ", meaning "Amon is the answer", and " ", meaning "Follow Amon".