On the day of SAT, which continued to take place even in the era of zombies, high school girls drive themselves to the place of examination.

Hwa-ja has been raising three daughters alone in Busan after her husband passed away. One day, the second daughter Hye-young comes back to Busan after having continuous setbacks in Seoul. While spending time with her mom, she accidently sees a letter written in Japanese, which triggers her curiosity. She starts to ask Hwa-ja about her past life and gets to know new stories of her mother that she had never heard of.

Yunhwa, who works at a shipyard to manage their livelihood after her husband′s accident, receives a notice of unfair dismissal. To make matters worse, their relatives suddenly come and try to take away the family land. Her son loses a large sum of money with Bitcoin, and her daughter dreams of escaping to Seoul while giving up her studies.