It was not very many minutes more before there was a dark, shadowy form, stealing in by the eastern sally-port, and hugging closely the black shadows of the wall. He paused, whoever it was, when he reached the area, and waited, listening. The sentry's tramp grew clear and then died out again, which meant that the sentry was back in the hallway of the barracks, and then the shadowy form stepped out into the moonlight and ran swiftly and silently across the area and sprang up the steps to the porch of the building; and there he stood and waited again until once more the sentry was far away--then stepped into the doorway and crept softly up the stairs. The strange midnight visitor was evidently some one who knew the place.