Young-joo, who is focused on adjusting to her new job, grows tired of the constant complaints of her boyfriend, Jae-yoon, who's serving in the anti-aircraft unit at 77 A Tower. She breaks up with Jae-yoon, and he accepts the breakup with a heartfelt voice message. Upon hearing this, Young-joo heads to the tower to meet Jae-yoon, but on her way there, she encounters an unexpected incident.

Jae-yoon and his direct junior, In-ho, head down to Eden Hotel, right below their air defense unit, for an errand. Upon arrival, they find a plane crashing into the heart of Seoul, and the hotel turned into a bloody chaos. Meanwhile, Young-joo and Jin-wook also confront zombies and team up with Tae-shik, who happens to be passing by. Together, they begin their fight for survival.

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.