A romantic investigative drama about rookie detective Yoo-Ryung who solves cases with her overflowing sense of justice and exceptional spatial perception but always gets herself into trouble because of her rash actions. She meets the Wangsimni station constabulary chief, a man who avoids cases and seeks stability who always ends up cleaning up after the problems caused by Yoo Ryung and holds the key to solving the cases.
This drama shows crime that could happen to anyone on any given day and the Subway Police who protect citizens as they travel below ground. Mostly, they deal with pickpockets and sexual harassment, but newbie Officer Yoo Ryung is after a much bigger case.