In the midst of a deadly pandemic triggered by a violent and zombie-like virus that has already devastated the United States and North Korea—with 150K infected and 30K dead in the U.S. and a staggering 8.5 million infected in North Korea—a man awakens in a blood-soaked motel room in Seoul. He discovers a cross-shaped scar on the back of his head, yet he has no recollection of who he is or why he is there. His solitude is shattered when armed CIA agents burst in, demanding to know the whereabouts of Dr. Jung Byung-ho (Jung Jae-young), who has been missing for 19 days along with his daughter while attempting to reach North Korea.
Confused and frightened, the man learns from a mysterious feminine voice within his ear that his name is Carter (Joo Won). To survive, he must heed her instructions. Guided by this disembodied voice, he escapes the motel and confronts countless attackers in a public bath, showcasing impressive combat skills that help him prevail against overwhelming odds.
Inside a van filled with NIS agents led by Choi Yu-Jin (Byeon Seo-Yun), Carter learns that the voice belongs to Han Jung-Hee (So-ri Jung), a member of North Korea's Labor Party. This group is collaborating with South Korea on developing a treatment for the rampant virus. The project revolves around an antibody derived from the infected daughter of Dr. Jung, known as Ha-Na (Kim Bo-Min). Following the revelation that Ha-Na and her father may have been kidnapped by the CIA—a plot that North Korea blames on South Korea—Carter's mission becomes clear: he must rescue Ha-Na and return her to North Korea for the vaccine production.
As Carter grapples with his identity and the mission's stakes, he learns that he was a naturalized North Korean citizen who fell in love with a North Korean woman and volunteered for this mission to save his own child. Unfortunately, he uncovers that the CIA believes he is actually Michael Bane, a supposed operative who died during a mission in Syria. Danger intensifies when Carter's molar is tracked by the CIA, leading to a scene where Jung-Hee warns him that it's rigged to explode, providing a narrow window for escape.
The political tension escalates as news reports claim that Dr. Jung Byung-ho has reached the North Korean facility. When Agent Agnes (Camilla Belle) approaches Carter under the guise of promoting trust, her warning ends in tragedy as she is shot. As Ha-Na is taken prisoner by the CIA, Choi Yu-Jin faces fatal consequences attempting to rescue her. In a race against time, Carter fights back and finally manages to reach Ha-Na, using Agnes's earpiece to learn that his identity as Michael Bane has been exposed.
With both urgency and resilience, Carter is guided to an airstrip where he must contend with pilots infected by the virus. When treachery leads to a shootout, Carter learns that a North Korean medic working for the CIA intended to betray him and Ha-Na. In a gripping confrontation, Carter leaps into action just as chaos erupts with infected pilots attacking the crew and passengers. He evades the carnage and secures Ha-Na, but their troubles are far from over.
Upon arrival in North Korea, Carter and Ha-Na are met by General Kim Jong-Hyeok (Sung-Jae Lee) and his forces, where a coup begins to unravel. As betrayal takes hold, General Kim seeks to exploit the situation, preventing their escape and aiming to utilize the virus against South Korea and the U.S. Carter’s resolve grows as he dodges assassination attempts, learning that Jung-Hee is his wife while battling through conflict alongside Dr. Jung to rescue their daughter Yoon-Hee.
In a heart-stopping sequence, Carter, Jung-Hee, and Dr. Jung, along with Ha-Na, barely escape a facility under siege, making their way towards a train that’s transporting infected individuals. With a critical decision to stop the train or risk a global outbreak, the stakes heighten. As they face relentless pursuit, Carter finally regains his memories - revealing he had willingly blocked them to protect his family who were imprisoned due to his former CIA alignment.
As the narrative unfolds, the tension culminates in a fierce battle aboard the train against North Korean soldiers. In the climactic moments, General Kim resurfaces, leading an assault against them. But amidst the uproar, Yoon-Hee awakens, seemingly cured of infection. In a final showdown, Carter successfully eliminates General Kim, only for the train to face disaster as an explosion takes place at a critical juncture, leaving everyone questioning the extent of survival amidst the chaos.
