Su Wantang is suspended after insisting on due process during an arrest and defying her superior's orders. Calm and rational by nature, she nevertheless carries a deep wound: her younger sister disappeared five years ago in an unsolved case, and her whereabouts remain unknown. On the day of her suspension, Su receives an anonymous letter directing her to take on the “Case Zero” cold case in the lowest level of the police station archives. The details in the file closely match her sister's disappearance. Forced to investigate in a private capacity, she discovers that every lead points to a corrupt network inside the police station.
The former forensic pathologist had his license revoked after a botched examination and now works as an embalmer at a funeral home. He appears flippant and carefree, but has an astonishing eye for detail and can spot things on a corpse that others miss. He is the son of the first person to discover the “Case Zero” crime scene. His father was framed and driven to suicide over the case, and he has spent years secretly investigating it. He first meets Su Wantang in the morgue. They join forces over their shared goal, but Gu Chenzhou continues to conceal the crucial piece of physical evidence he possesses.
