The South Korean Military and Police forces try to contain the spread of Lytta and Next through extensive investigation and authoritative quarantine measures, while civil rights groups protest against them, believing the infected are still capable of normal human interaction.

However, in order to do so, she must be married, so she asks her high school friend Jung Yi-hyun (Park Hyung-sik), a former star baseball player but now a police detective, and he agrees to a contract marriage.

Class discrimination is evident where the upper floor resident Oh Yeon-ok (Bae Hae-sun) struggles to be the apartment representative while keeping everyone in check.

Through Jung Yi-hyun's detective work, he encounters a diseased person who he believes became this way due to a failed pneumonia drug called Next, which had been widely circulated in order to promote attentiveness and strength.

This assumption is later confirmed when a resident member who consumed the drug, secretly sold to her in the building's gym, ultimately becomes infected with the mad person disease and succumbs to the illness.

Han Tae-seok initially tries to keep the mad person disease a secret, but with more cases progressing and people getting panicked, it is revealed to the public.

Ahn Gil-ho has worked on numerous hits such as Record of Youth, Memories of the Alhambra and Stranger, while writer Han Sang-woon has also penned The Good Wife, the Korean remake of the 2016 American TV series.