Y/n isn't just an ordinary college student. At just twenty, she's already working as an undercover detective, known only by her code name: ZERO. With a mind sharper than most, she solves the cases that seasoned officers can't. The world doesn't know her face, and the police intend to keep it that way. But hidden in the shadows is a name that chills even the bravest to their core WINTER. A serial killer who leaves behind bodies and fear wherever she goes. What no one knows is that Winter isn't just a faceless nightmare. She's Minjeong Y/n's best friend. Two secrets. Two double lives. One hunting for justice. One craving obsession. As Winter's killings escalate in a twisted game to uncover ZERO's identity, Y/n races to solve the murders... never realizing the monster she's chasing just right beside her.