Contains spoilers for this episode and earlier episodes.
Cheong-san pulls On-jo out of danger as the cafeteria collapses into panic. They fight through the corridors and join classmates sheltering in a classroom, but the refuge lasts only until Coach Kang arrives. His bitten arm makes the students suspicious, and he soon turns and bites Min-ji. Dae-su uses a door as a shield while Su-hyeok helps the group force a passage through the infected students blocking their escape.
At the police station, Byeong-chan's account and his recorded experiments connect the outbreak to his attempt to help Jin-su resist bullying. Hyeon-ju's arrival at hospital carries the infection beyond the school, leaving emergency services overwhelmed. On-jo reports a fire because she believes that will bring her firefighter father to help. Meanwhile, English teacher Park Sun-hwa reaches the broadcasting room and urges surviving students to find somewhere safe while violence spreads across the grounds.
On-jo loses her closest friend when I-sak begins showing symptoms. She cannot accept what is happening and tries to hold onto her, but must finally let her fall from the window to protect the others. With their room no longer secure, the students use a fire hose to climb down toward Sun-hwa. Cheong-san waits upstairs so On-jo can descend first. The infected break through before he follows and knock him out of the window, leaving his fate unresolved.