Black garbage bags filled with dismembered body parts begin to pop up around the city: in an elevator, on a highway, at the edge of a basketball court. The victims are nearly impossible to identify. The killeršs motive is a complete mystery. Leading the investigation is Detective Cho (Han Suk-gyu), a burnt-out cop trying to redeem his tainted reputation with this case. Setting up a special crime investigation unit dedicated to these gruesome murders, Cho and his partner, the veteran Detective Oh (Chang Hang-sun) map out the order of the murders, interchanging the body parts like pieces in a grotesque puzzle.

A break opens up in the case when Cho is led to a beautiful and enigmatic young artist. Su-yeon Chae (Shim Eun-ha), with whom all the victims have had relations. But aside from this lead, Cho is far from solving the case. Still without a motive, Cho is grasping for clues. While being drawn closer to the mysterious Su-yeon, he begins unraveling her tortured past, leading to new questions and suspects. Cho decides to investigate her late college classmate and current colleague Ki-yeon.

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 early the next morning Detective Cho is notified of the fourth murder. Under the rainy urban landscape of Koreašs capital, another garbage bag is discovered on a highway. This time, the corpse is a headless Ki-yeon...