In a dramatic opening, a highly skilled female assassin is captured by the South Korean intelligence agency after a bloody rampage to avenge her father's death. Recognizing her lethal skills, the agency fakes the assassin's death and offers her a choice: work for them for ten years, or face lifelong imprisonment. Seeking a chance for freedom and a new life, she reluctantly agrees and is given a new identity. Under the constant surveillance of her handlers, she undergoes rigorous training and is promised her freedom once her service is complete. In this time, she meets and begins to fall for a fellow agent who genuinely cares for her, providing a glimpse of normalcy and affection she never experienced before.

The past, however, is never truly behind her; it relentlessly collides with her attempts at a new beginning. The agency sends her on various assassination missions, testing both her commitment and skills. As she tries to protect her newfound life from collapsing under the weight of her former one, intricate layers of betrayal and revenge are revealed. Deeply entrenched in a web of deception, she must navigate through allegiances and enmity. The harrowing journey forces her to confront both her blood-soaked history and uncertain future, leading to unforeseen consequences and intense confrontations.