Upon the floor, and at intervals in the wall immediately behind, were certain tiny green buttons, practically unnoticeable, which on being pressed permitted a soothing and persuasive narcotic to rise invisibly about the occupant of the chair.  The effect upon the excitable patient was rapid, admirable, and harmless.  The green study was further provided with a secret spy-hole; for John Silence liked when possible to observe his patient’s face before it had assumed that mask the features of the human countenance invariably wear in the presence of another person.  A man sitting alone wears a psychic expression; and this expression is the man himself.  It disappears the moment another person joins him.  And Dr. Silence often learned more from a few moments’ secret observation of a face than from hours of conversation with its owner afterwards.

A very light, almost a dancing, step followed Barker’s heavy tread towards the green room, and a moment afterwards the man came in and announced that the gentleman was waiting.  He was still pale and his manner nervous.

“Never mind, Barker” the doctor said kindly; “if you were not psychic the man would have had no effect upon you at all.  You only need training and development.  And when you have learned to interpret these feelings and sensations better, you will feel no fear, but only a great sympathy.”

“Yes, sir; thank you, sir!” And Barker bowed and made his escape, while Dr. Silence, an amused smile lurking about the corners of his mouth, made his way noiselessly down the passage and put his eye to the spy-hole in the door of the green study.

This spy-hole was so placed that it commanded a view of almost the entire room, and, looking through it, the doctor saw a hat, gloves, and umbrella lying on a chair by the table, but searched at first in vain for their owner.

The windows were both closed and a brisk fire burned in the grate.  There were various signs—­signs intelligible at least to a keenly intuitive soul—­that the room was occupied, yet so far as human beings were concerned, it was empty, utterly empty.  No one sat in the chairs; no one stood on the mat before the fire; there was no sign even that a patient was anywhere close against the wall, examining the Bocklin reproductions—­as patients so often did when they thought they were alone—­and therefore rather difficult to see from the spy-hole.  Ordinarily speaking, there was no one in the room.  It was undeniable.

Yet Dr. Silence was quite well aware that a human being was in the room.  His psychic apparatus never failed in letting him know the proximity of an incarnate or discarnate being.  Even in the dark he could tell that.  And he now knew positively that his patient—­the patient who had alarmed Barker, and had then tripped down the corridor with that dancing footstep—­was somewhere concealed within the four walls commanded by his spy-hole.  He also realised—­and this was most unusual—­that this individual whom he desired to watch knew that he was being watched.  And, further, that the stranger himself was also watching!  In fact, that it was he, the doctor, who was being observed—­and by an observer as keen and trained as himself.