When Catherine (Jade Leung), a mentally disturbed young woman, is detained by the police after accidentally killing a truck driver, she finds herself part of a covert training system. Programmed as an assassin, having learned a host of new deadly skills, she becomes a lethal government weapon, codenamed Black Cat.

Catherine, a troubled woman, is recruited by the government for assassin training under the code name "Black Cat". Proficient in her role, she struggles with her newfound love interest and commitment to the agency.