Sergeant Kim Seonyeob, nearing the end of his military service, quietly volunteers for night duty at the 1-1 guard post to dodge a grooming inspection. He's paired with Private Park Jihoon, a fresh-faced recruit. Their uneventful shift takes a sharp turn when the keen-eyed officer Park Jang-hyun makes an unexpected visit. As Kim Seonyeob's expression grows increasingly rigid, the secrets he's been hiding slowly rise to the surface…