A series of black garbage bags filled with dismembered body parts begin to show up around the city: in an elevator, on a highway, at the edge of a basketball court, and rendering the victims nearly impossible to identify. The killer's motive is a complete mystery. Leading the investigation is Detective Cho, a burnt-out cop trying to redeem himself with this case. Setting up a special squad dedicated to these gruesome murders, Cho and his partner, the veteran Detective Oh, map out the order of the murders, interchanging the parts like pieces in a grotesque puzzle. Mystified by the surgical precision of the dismemberments and finding a medical antiseptic called "Hexamedrin" spread all over the bodies, the detectives start suspecting a doctor or a biologist as the killer. A break opens up when Cho is led to a beautiful and enigmatic young artist, Chae Su Yeon, whom all the victims have had relations with. But besides this revealing breakthrough, Cho is far from solving the case. Still not having found a motive, Cho is grasping for many clues. As the murders continue, Cho is drawn closer to Su Yeon and begins unravelling her tortured past, leading to new questions and suspects. Cho and Oh subsequently discover that her father, a famous painter, mysteriously disappeared years before. Cho decides to investigate her late college classmate and current colleague Ki Yeon, and her friend, Sung Min. While Cho questions Ki Yeon, the fragile Su Yeon is attacked but manages to escape. After being released from police custody, Ki Yeon disappears, and the next morning Detective Cho is notified of the fourth murder. Under the rainy urban landscape of Korea's capital, another garbage bag is discovered on a highway. This time, the corpse is a head-less Ki Yeon.
