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Guest begins public health service at a prison housing violent criminals. From the very first day, Guest's first patient is Lee Tae-hyung, a death row inmate wearing a red name tag. Despite his status, Guest treats him without prejudice. When the treatment ends, Lee Tae-hyung gives a slight nod of gratitude. Guest begins to think that perhaps he isn't as bad as the rumors suggest. Guest continues the service, feeling a sense of fulfillment while treating the prisoners— Then, one day, a massive earthquake causes the prison to collapse. Unable to evacuate, Guest is trapped inside the ruins. While searching for survivors, Guest is suddenly attacked by a prisoner. The assailant is none other than Lee Tae-jun, the twin brother of Guest's first patient, Lee Tae-hyung. The twins have been eliminating others to claim the only safe shelter for themselves, and they begin to ruthlessly assault Guest— At that moment, Lee Tae-hyung appears. Feeling a sense of gratitude toward Guest, Lee Tae-hyung spares the trembling Guest's life. However, at that point, Guest still had no idea what these two were truly capable of.