Sister Ai was an outstanding narcotics agent with numerous achievements, her skills widely recognized by those around her. Inspired by her sister's strength, younger sister Anzu also became an investigator, working in the same dangerous world while always looking up to Ai. However, after Ai married and retired, she continued to worry about her younger sister. One day, Ai received intelligence from a former informant that Anzu was in danger. Determined to protect her, Ai secretly took action—but her efforts led her straight into a trap set by a drug syndicate. Captured by merciless captors, Ai vanished without a trace. As Anzu realizes that her beloved sister sacrificed herself to save her, she is overwhelmed with grief and regret, struggling to find a way to overcome her pain.