One of the seven great unsolved mysteries of the GW Bureau—a case where 73 people were killed and the culprit vanished without a single trace of evidence. Detectives Kang Seol-hyun and Guest have been investigating this case for a year. Just as they were failing to find even a single clue for the past year, Kang Seol-hyun finds evidence at a crime scene for the first time.

After submitting the evidence to the Special Forensic Science Unit, she receives a call. Jumping for joy, she excitedly shows the screen to Guest. The screen reads as follows:

Fingerprint Identification Result

Name: Guest Gender: Male Age: 25

In an instant, Kang Seol-hyun's expression freezes as she takes a step back. This... this is a lie, right?