Sinb is an expert at cracking every cases she solves, along with her best friend and partner, Jung Yerin but one day, Sinb couldn't help but tell the chief to give the mysterious 5 year old case to her. 

           "Are you serious about this, Detective Hwang?"asked the Chief. "I know you're an expert but this case is super hard to crack! Lack of evidences and witnesses!"

            "Sir, maybe there are more of them that you ever think."said Sinb darkly. "or maybe you're talking to the wrong person but Sir! Give me a chance, I can solve this."

            The Chief sighed. "Okay, I'll give you the case"said the Chief. "But I want to hear that you're making progress with this case, Understand?"Sinb nodded. "Good, here it is"

             The Chief stood up and went to a drawer, he checks every files until he saw the name of the case: The Mysterious murder in Gangnam-gu.

             He grabbed the file and went back to his desk, handing the file Sinb. "Good luck, detective. I hope you crack and manage to track the mastermind behind this disgusting murder"said the Chief. 

              Sinb nodded. "I will Sir, you can count on me"said Sinb before leaving the office. 

              She walked down the hallways of the department and met Yerin along the way. "So, you got it?"asked Yerin. "Yeah, and we need to start now!"said Sinb, opening the door to her office. 

              "Like right now, now?"Yerin said, sitting on one of the chairs in Sinb's office. "Of course, Yerin-unnie! This is a serious case, and the Chief is looking forward for us to make progress!"said Sinb seriously, placing the files down and reading them one-by-one.

                "Okay, okay!"Yerin grabbed one of the papers and started reading and examining the words. 

        The Mysterious murder in Gangnam-gu 

On September 23, 2012, nearby people at the crime scene reported screams and crashing at exactly 3am inside a house of a family of 5. The police came 30minutes later with the suspect already escaped and lack of evidences to find. The police only found a piece of paper written with "I'm sorry" and an accessory belonging to one of the victims. 

The police tried to make what had happen and what did the suspect had did to them, but it was tricky. The police just left with the bodies to take them to forensics. Ever since then, the police never went back to the crime scene ever again. 

             "Are you thinking what I'm thinking?"Yerin asked. Sinb looked up, irritated. "No."said Sinb. Yerin pouted. "I think this is kind of connected to Umji's disappearance!"Sinb raised her eyebrow. "What are you talking about? Umji's disappearance happened in Ilsan. We're taking the case of Gangnam-gu, unnie"Yerin frowned and just continued to read the file. 

             Sinb continued reading too. After a moment, Yerin spoke up again. "It's just a possibiliy, maybe it's connected or such"said Yerin convincingly. Sinb sighed. "Yerin-unnie, let Eunha-unnie do her own work."

             "But it has been 5 years since Umji disappeared! 5 years! Same night with our case right now!"Yerin stood up from her seat. 

              "It's a possibility that it is indeed connected."

               Sinb rubbed her temple, sighing. "Unnie, I know your goddamn worried about our best friend but we can't do such thing, Eunha-unnie has it in control."

               "Are you not worried?"

               "I'm still worried about her unnie"

                Yerin just sighed and went back to seat on her chair. "Let's just continue."Sinb nodded and went to get the folder with the pictures of the crime scene. "I'm bothered that they didn't knew the victims' names"said Sinb. 

                 Sinb almost puked when she saw the first picture she took out. 

                 The picture shows the crime scene where four of the victims are laying down. A girl who's almost-opened back and bashed head can be seen, laying next to the couch where a boy with no eyes, wounded face and slit throat is laying. On the ground, a man who's head is bashed also can be seen with an woman who was gunned down beside him, on the head, stomach and legs. 

                "Oh god... How can a person do this... Unnie..."she froze upon seeing the second picture. It was Umji, on the bathtub, gunned down and was left in her pool of blood. "Why? What is--"Yerin froze too upon seeing it.