A third woman’s body is found at an abandoned factory, a strange knot tied around her wrist. Criminal investigation captain Cheng Yu is forced to seek help from a top criminal psychologist, only to face the most painful surprise of his life: the person assisting with the case is Lin Muqing, the lover who left without a word three years ago.
They were soulmates in college, but a fatal misunderstanding during an undercover operation tore them apart. Now reunited, she is a cool-headed profiler who dissects a killer’s psychology, while he is a hard-nosed cop who believes only in evidence. When Lin Muqing points out that the knot conceals a code for surgical procedures, and Cheng Yu uses his investigative expertise to uncover the truth behind a string of jurors’ murders, they have no choice but to join forces to hunt down the killer.
But their old wounds have yet to heal when another case emerges. The killer with the knots suddenly escalates his attacks, and under threat of death, Lin Muqing recognizes him: the son of a nurse who died in a medical malpractice case. His revenge list targets those who handed down the verdict. On a rainy night atop a high-rise, they face off in a struggle for life and death. To save her, Cheng Yu reveals the secret he has kept buried: he disappeared three years ago to investigate an even larger pharmaceutical scandal behind the case.
When the mastermind turns a poisoned blade on Lin Muqing’s loved one, she uses herself as bait and plunges into the trap. Cheng Yu fights his way through the flames and rescues the woman he loves, only to fall into an even darker web: the knot’s poison spreads through his arm, and the real culprit is none other than Lin Muqing’s mentor, the eminent criminal psychology professor Chen.
At the medical school graduation ceremony, her former mentor sets a deadly trap. The knot, once a symbol of crime, has become an instrument for controlling the human mind. To put an end to this deranged experiment carried out in the name of justice, Lin Muqing turns the psychology he taught her against him, while Cheng Yu uses his own body to shield her younger sister from a blade.
