Inspector Koo follows Koo Kyung-yi, a former police officer who becomes a reclusive insurance investigator. Living a messy life filled with video games and alcohol, she is suddenly pulled back into the investigative world when she realizes a series of mysterious, seemingly accidental deaths are actually calculated murders orchestrated by a cunning university student. Driven by her sharp intuition and relentless obsession, Kyung-yi embarks on an unorthodox and darkly comedic pursuit of the mastermind, blurring the lines between justice and madness.