At a prep school, a secret horror begins to unfold as the students begin to die.

Delivery man Dong-soo has a tic disorder that causes him to say inappropriate words he doesn't mean. Online novelist Ye-ri has closed herself in her apartment ever since her sibling's death. Twice a week, Dong-soo makes deliveries to Ye-ri and they develop a quiet bond, talking about things they've never told anyone else. Ye-ri reveals that it was her late sibling's wish to see a sea without water, and Dong-soo decides to fulfill that wish for her.