In 2024, political and territorial disputes between
China,
Japan, and South Korea lead to Japan remilitarizing and the
United States and
Russia moving to secure their interests in East Asia. Fearing the possibility of war, North and South Korea agree to reunify for the sake of survival within five years. However, this leads the other aforementioned powers, who oppose the reunification, to impose significant
tariffs against the Koreas, sparking an
economic depression that causes pro-reunification sentiment to plummet and leads to spikes in
civil unrest,
crime, and
terrorism. With anti-reunification movements swelling to the point of the formation of the
domestic terrorist group "the Sect", the South Korean government, seeing the
National Police Agency is unable to handle the protests and terrorism alone, forms the Special Unit to counter the Sect, heavily arming and equipping its soldiers with futuristic
powered exoskeletons and distinctive
gas masks with glowing red lenses. Though the Special Unit is effective in crushing the Sect, an incident a year after their formation known as "Bloody Friday"—when a Special Unit team mistook young schoolgirls for Sect terrorists during a raid, killing 15 of them—sparks massive backlash and forces Special Unit soldiers to always wear their gas masks on deployment to protect their identities. Additionally, the Special Unit finds themselves at odds with the Public Security Department, an
intelligence unit that wishes to dissolve the Special Unit. In 2029, an anti-reunification protest at
Gwanghwamun Plaza in
Seoul turns violent when Sect terrorists attack
riot police lines with firearms and
satchel charges, killing several outgunned officers as well as protestors in the crossfire. The Special Unit is deployed to defeat the terrorists and raids their hideout in the
storm sewers below, killing most of the Sect terrorists when they refuse to surrender. Special Unit soldier Lim Joong-kyung confronts Lee Jae-hee, a young Sect courier carrying a satchel charge, and attempts to coax her into surrendering, but she detonates it instead, killing herself. News of the incident damages the Special Unit's reputation even further, and a shaken Lim is sent back to training for reevaluation under
drill instructor Jang Jin-tae. Lim is contacted by Public Security head Han Sang-woo, who informs him that the deceased courier has a sister, Lee Yun-hee. Lim meets Yun-hee at the
Namsan Tower; she tells him she does not hold Lim responsible for her sister's death as they were merely fighting on opposing sides, and they quickly befriend each other. Unbeknownst to Lim, Yun-hee is actually a former Sect courier who, to avoid a prison sentence and to secure a medical operation for her ill brother, has reluctantly been roped into working with Han and Public Security in their plot to discredit the Special Unit; however, the Special Unit is secretly already aware of this, and an internal deep-cover group known as "Illang" ("Wolf Brigade" in English) is seeking to protect them from Public Security. Yun-hee is captured and interrogated by Illang member Kim Cheol-jin, and reveals that the Sect is being funded by Public Security and that she was blackmailed into killing for them. Yun-hee is released and goes to the location of Public Security's trap at the Namsan Tower, where she is to incriminate Lim while carrying a
tracking device for undercover Public Security agents to arrest him; however, Lim is alerted to the agents' presence, kills them, and escapes with Yun-hee. After escaping, Lim sends Han photographic evidence of Han's involvement with the Sect, prompting Public Security to launch a
manhunt for them, while the Special Unit raids a government building in retaliation for Public Security's activities. Lim and Yun-hee attempt to reach a
safe house to meet with Illang and their leader, Jang, but they are unable to reach it and take refuge in the sewers instead, while Kim is captured, brutally interrogated, and accidentally killed by Han. While in the sewers, Yun-hee activates her tracking device, alerting Han and Public Security who dispatch their own
special forces squads to her location. Illang arrives and provides Lim with a Special Unit exoskeleton and machine gun before taking Yun-hee—revealed to actually be Kim Seo-hee, former commander of the Sect's women's unit—to safety. The Public Security squads and Han converge on the location of Yun-hee's tracking device but are met by a fully armed and armored Lim, who kills the squads and Han in a lengthy
shootout. Lim reunites with Seo-hee and the rest of Illang, but Jang orders him to execute Seo-hee, as she is still a terrorist who spied for Public Security. However, Lim refuses and frees her when Jang departs. Expecting this to happen, Jang lets Seo-hee live and returns to battle Lim for his betrayal, but allows him to leave when Lim announces he is retiring from the Special Unit. Later, Seo-hee and her brother board a train to leave Seoul; as the train departs, Seo-hee looks out the window and sees Lim. ==Cast==