Read it through once

What was that? In the silence he heard a gentle scratching sound—low, but very distinct in the quiet of the night. It came from the door of the house. Ferrier crept into the hall and listened intently. There was a pause for a few moments, and then the low insidious sound was repeated. Someone was evidently tapping very gently upon one of the panels of the door. Was it some midnight assassin who had come to carry out the murderous orders of the secret tribunal? Or was it some agent who was marking up that the last day of grace had arrived. John Ferrier felt that instant death would be better than the suspense which shook his nerves and chilled his heart. Springing forward he drew the bolt and threw the door open.