As a teen, prosecutor Hwang Shi Mok received surgical treatment for his hypersensitivity to sounds, but the procedure left behind serious side effects.
Shi Mok begins looking into a new, unexpected suspect, but he must tread lightly. Yeo Jin is ordered to report on any information Shi Mok has gathered.
Yeo Jin secretly follows Prosecutor Seo, hoping to learn more about his association with Ga Young, but Prosecutor Seo soon sets his sights somewhere else.
Shi Mok's non-reaction to the latest murder puzzles those around him, but it begins to affect him unexpectedly. The police try to determine if they're dealing with a serial killer.