In the fictional Republic-era Dongwan Port, reborn quarantine medical officer Shen Yanzhou returns to the critical turning point of an epidemic outbreak. A returning student intentionally conceals their itinerary in an epidemic area, disguising a common insect bite to sneak through customs. Shen Yanzhou strikes the bronze bell to initiate emergency quarantine, but faces pressure from powerful figures and tabloid smear campaigns. He teams up with the quarantine team to gather physical evidence and trace the source of infection, holding the line at the port amidst misunderstandings and crises. Yet the hidden vector threat has not been eradicated, and greater risks are lurking in the shadows, waiting for an opportunity.