Captain Tremayne turned the corner, and was out of my sight, seeing that I didn't go beyond the guardroom doorway." Sir Terence's lips parted with a snap of impatience.

"But you must have heard," he insisted.

"You must have heard his steps--whether they went upstairs or straight on." "I am afraid I didn't take notice, sir." "But even without taking notice it seems impossible that you should not have heard the direction of his steps.

Steps going up stairs sound quite differently from steps walking along the level.

Try to think." The sergeant considered again.