20 years ago Moo-Yeom’s father was a suspect in the "Gap Dong” serial murder case. Because of the detectives’ oppressive investigation, Moo-Yeom’s father killed himself. Now, Moo-Yeom is a detective and works to capture the killer Gap Dong. The statue of limitations has expired for the serial murder case and Moo-Yeom resigns to the belief that Gap Dong is dead. New clues though for Gap Dong appears in front of Moo-Yeom and he sets out to catch him once and for all.
Mu-yeom who became a detective for his father, receives news like a nightmare.
Hearing something suspicious about the body of a murder case, Mu-yeom rushes to the crime scene.
It's reported that the first case is the act of Gabdong and there will be a second case of murder.
Mu-yeom is arrested as a criminal, and Yang suggests to compare the DNA of Gabdong and Mu-yeom.
Chief Yang meets Maria and thinks of a girl he met at the scene for a case from a while ago.
Mu-yeom suspects Tae-oh as Gabdong. Tae-oh lets out the story of his dead father to Maria.
The civilians blast anger and attack the police for failing at preventing the fourth case.
Mu-yeom kidnaps Ji-ul and tracks down Tae-oh, with the predicted date for a fifth case approaching.
After finding a corpse, Mu-yeom runs at Tae-oh, and Maria witnesses something shocking.
A phone call rings from the real Gabdong. Mu-yeom finally gets to know the true identity of Gabdong.
Gabdong is finally caught. Mu-yeom starts the interrogation and goes to get his shut mouth talking.
The plane the murder happened at, which Tae-oh was in, makes a flyback.
Tae-oh confesses his crimes, and Maria is shocked after finding out that Gabdong's probably dead.
After finishing the montage, Maria turns the young Gabdong montage into Gabdong of the present.
Mu-yeom and Tae-oh, neither one of them slows down and races to the end of the cliff.
Mu-yeom interrogates to prove Do-hyeok as Gabdong. He gets closer to the secret of the Murder case.
While searching Do-hyeok's house, Mu-yeom finds a suspicious picture frame of the Eiffel Tower.
Tae-oh starts a deal between Do-hyeok and Maria. Mu-yeom notices and makes the two Gabdong gather.
A gunshot rings at the pool Mu-yeom and Do-hyeok are at, and someone falls bleeding.
The trial of the two Gabdong finishes, with hard choices to make, the two fall into a great dilemma.
