Young-joo, che sta cercando di ambientarsi nel suo nuovo lavoro, è stufa delle continue lamentele del suo ragazzo, Jae-yoon, un soldato dell’unità antiaerea di stanza nella Torre 77 A. Lei lo lascia e lui accetta la separazione con un commovente messaggio vocale. Dopo averlo ascoltato, Young-joo si dirige verso la torre per incontrarlo, ma per strada ha un incidente inaspettato.

Jae-yoon e il suo sottoposto, In-ho, vanno a fare una commissione all’Eden Hotel, l’hotel sotto la base dell’unità di difesa aerea. Al loro arrivo vedono un aereo schiantarsi nel centro di Seul e nell’hotel il caos regna sovrano. Nel frattempo, anche Young-joo e Jin-wook affrontano gli zombie e si uniscono a Tae-shik, che stava passando di lì. Insieme iniziano a lottare per la sopravvivenza.

Soo-Jeong and chef Jung from the Eden Hotel, Jae-Yoon, and In-Ho manage to return to the military unit. The find out the base they thought was safe begins to face the threat of zombies. Young-Joo sees the text messages sent by Jae-Yoon.

In the midst of the zombie crisis, Jae-yoon and Young-joo reminisce about their happy past and long for each other even more. Meanwhile, Jae-yoon and his squad mourn the loss of their comrades but find relief in the news of a supply helicopter's arrival. Young-joo’s group encounters Tripeater, who has been bitten by a zombie but has not yet turned.

After downing the supply helicopter, First Sergeant Jung Tae-hwa realizes that survival at their station is impossible. He plans to lead his platoon in an escape from the zombie-ridden A Tower. Meanwhile, Young-joo's group finally reaches the gate of A Tower, only to be greeted by a horde of zombies.

Young-joo is left by herself at the Express Bus Terminal Station, but a stroke of luck leads her to a metro staff office, where she gathers supplies to battle the zombies. Meanwhile, Jae-yoon's group reaches Eden Hotel, where they run into Arron Park, who has survived there alone. But the group gets split up by an unexpected attack by the zombies, throwing them into separate hotel rooms.

On her way to Suseo Station, Young-joo meets a very special person, who helps her reminisce on the good memories with Jae-yoon. She relentlessly fights the zombies alone on her way to Jae-yoon. Meanwhile, Jae-yoon and the squad successfully reach the 35th floor through the ducts, but they must find another way down to the first floor.

Jae-yoon escapes the A Tower first and saves others with a brilliant idea. But they must endure another goodbye. In the meantime, Young-joo runs into people who are even more brutal than zombies. Will Jae-yoon and Young-joo, the two lovers fighting their own separate battle, finally reunite in this chaotic apocalypse?