1. On the first day of school, Shen Zhao approaches Song Zhixia and invites her to join the biology club. But when he touches her mask, his pupils suddenly contract.
2. Song Zhixia notices that Shen Zhao disappears promptly at 5:00 p.m. every day. She follows him to an abandoned laboratory building and overhears him talking to a professor: "Sample A07 is beginning to show a rejection response."
3. The key conflict: Song Zhixia catches Shen Zhao injecting himself with drugs after cutting himself in the lab. He grabs her by the throat and threatens her: "If you don't want to die, pretend you know nothing."
4. The twist: The list of fire survivors shows that Shen Zhao and Song Zhixia should both have died in the same accident, yet he has no burn marks at all.
