Detective Yang Shi-ohn wakes up from a six-year coma. She gets reassigned to the lost and found department, where she discovers that she's gained the supernatural ability to see ghosts connected to the objects left behind there. Along with her new partner, rookie cop Cha Gun-woo who's a hotheaded skeptic, Shi-ohn uses the information to solve cold cases. Gun-woo only believes in tangible things he can see, hear and touch, but he gradually comes to trust Shi-ohn, and together, the bickering partners help the spirits fulfill their dying wishes and unfinished business before passing on to the afterlife.

One of the ghosts watching over Shi-ohn is her ex-boyfriend Lee Hyung-joon, another detective who died that night six years ago when Shi-ohn received the serious head injury that nearly killed her and left her comatose. They were working on a big case together, but Shi-ohn has no memory of what happened that fateful night.