Prosecutor Hwang Shi Mok, who works in the Seoul Western Prosecutor's Office, finds a person-of-interest (CEO Park Moo Sung) murdered in their home. The suspected killer, Kang Jin Seop, is later apprehended with the help of Lieutenant Han Yeo Jin. Kang frantically claims he is not the killer, but shocking amounts of circumstantial evidence implies otherwise. He is tried and sentenced to 22 years in prison, partly thanks to prosecutor Young Eun Soo's strategic presentation of evidence. Kang later hangs himself in a prison cell and leaves a suicide note in which he maintains his innocence. The note also accuses the prosecution of wronging Kang by manipulating the evidence. Hwang immediately reopens the investigation, only to discover ongoing implications of fraud and corruption.