As a teen, prosecutor Hwang Si-mok received surgical treatment for his abnormally developed brain, but the procedure left behind serious side effects.

The convict's strong plea for his innocence prompts Si-mok to review the CCTV clip. At the Yongsan police station, he runs into officer Han Yeo-jin.

Si-mok, puzzled by the details of the most recent murder case, visits the victim's home to seek more clues. Yeo-jin joins him in the investigation.

New pieces of evidence only increase the list of possible suspects. In the midst of the confusion, a few begin to question Si-mok's innocence.

Si-mok selects key lawyers and police officers to be part of the special investigations team. Their probe begins with Dong-jae as the starting point.

Returning home from the rooftop party, Si-mok discovers that an intruder has left something in his bedroom. Yeo-jin and Geon come over right away.

Yeo-jin collects evidence as Si-mok interrogates the suspect. Many questions get answered, but the most important problem of all remains to be solved.