Binhai City is a city of prosperity and darkness. Three years ago, the "Blood Butterfly Serial Case" shocked the whole city. All the deceased had butterfly patterns tattooed on their chests, but the case became a mystery due to insufficient evidence. Female forensic doctor Han Han (28 years old) is obsessed with identifying insect traces because she witnessed her mother die in a similar way when she was young; Interpol Captain Leng Yi (32 years old) was once the person in charge of the case, but he suffered a psychological shadow due to the sacrifice of his partner. The two reunited due to a bizarre corpse dismemberment case. During the case, they went from confrontation to cooperation, and gradually uncovered the criminal network "Shadow Butterfly" that spanned ten years - an underground organization that uses gene editing technology to create "perfect killers".
