It has been about a year since Korra returned from the spirit world with Asami and things aren't looking so great since then. A new religious group known as the Iron Bloods have brought havoc within Republic City as many citizens have been kidnapped and have gone missing since her return. Many things about the cult remain a mystery, but there are some things that Korra and her friends were able to discover ever since they began investigating.
For starters, the Iron Bloods believe that all technological advancements for the past hundred years have been made possible because of a god-like entity known as the Omni-Messiah. The cult believes that the Omni-Messiah is present within every single machinery throughout the world as they regard it as the source of power that brings machines to life permeating within all moving machinery. The very idea that not worshipping this god-like figure is considered a sin and a threat to these believers, fearing that if they don't pray or sacrifice enough that one day, the Omni-Messiah would abandon this world, making all technological advancements completely naut.
With this propaganda in mind, the members of the religious cult, use blood sacrifices to satisfy and appease their god, believing that by doing so, will prevent their machines from malfunctioning. Some have gone even further and begun discarding their own living flesh and replacing it with metal and gears. This has become a challenging mission for the Chief of Police, Lin Beifong, as she is unable to figure out anything else about this organization. She is unable to figure out their origin, their next moves, or even the main purpose within her city. However, it has become especially hard for Korra's mental state as her recent mission in stopping the cult, resulted in her friends, Mako and Bolin, to be killed.
Ever since then, Korra has been traumatized by the incident and has discontinued her investigation in the cult and remains silent, sleeping her life away in the air temple. While Opal, Bolin's girlfriend and airbender, had forgiven Korra, Korra finds it hard to forgive herself and spends her day sleeping in bed or standing still, slowly losing her sanity.
Although Asami wants to help, Korra refuses to tell anyone what exactly happened on her mission with Mako and Bolin, remaining completely silent. With the Iron Bloods hiding within the shadows of Republic City, the world needs the Avatar more than ever.