On the corner opposite Dr. Stuart's establishment stood a house which was "to be let or sold." From the estate-agent whose name appeared upon the notice-board I obtained the keys—and had a duplicate made of that which opened the front door. It was a simple matter, and the locksmith returned both keys to me within an hour. I informed the agent that the house would not suit me.  
Nevertheless, having bolted the door, in order that prospective purchasers might not surprise me, I "camped out" in an upper room all day, watching from behind the screen of trees all who came to the house of Dr. Stuart. Dusk found me still at my post, armed with a pair of good binoculars. Every patient who presented himself I scrutinized carefully, and finding as the darkness grew that it became increasingly difficult to discern the features of visitors, I descended to the front garden and resumed my watch from the lower branches of a tree which stood some twenty feet from the roadway.
 
At selected intervals I crept from my post and surveyed the lane upon which the window of the consulting-room opened and also the path leading to the tradesmen's entrance, from which one might look across the lawn and in at the open study windows. It was during one of these tours of inspection and whilst I was actually peering through a gap in the hedge, that I heard the telephone bell. Dr. Stuart was in the study and I heard him speaking.
 
I gathered that his services were required immediately at some institution in the neighbourhood. I saw him take his hat, stick and bag from the sofa and go out of the room. Then I returned to the front garden of my vacant house.
 
No one appeared for some time. A policeman walked slowly up the road, and flashed his lantern in at the gate of the house I had commandeered. His footsteps died away. Then, faintly, I heard the hum of a powerful motor. I held my breath. The approaching car turned into the road at a point above me to the right, came nearer … and stopped before Dr. Stuart's door.
 
I focussed my binoculars upon the chauffeur.
 
It was the brown-skinned man! Nom d'un nom! a woman was descending form the car. She was enveloped in furs and I could not see her face. She walked up the steps to the door and was admitted.
 
The chauffeur backed the car into the lane beside the house.
 
My heart beating rapidly with excitement, I crept out by the further gate of the drive, crossed the road at a point fifty yards above the house and walking very quietly came back to the tradesmen's entrance. Into its enveloping darkness I glided and on until I could peep across the lawn.
 
The elegant visitor, as I hoped, had been shown, not into the ordinary waiting-room but into the doctor's study. She was seated with her back to the window, talking to a grey-haired old lady—probably the doctor's housekeeper. Impatiently I waited for this old lady to depart, and the moment that she did so, the visitor stood up, turned and … it was Zara el-Khala!
 
It was only with difficulty that I restrained the cry of triumph which arose to my lips. On the instant that the study door closed, Zara el-Khala began to try a number of keys which she took from her handbag upon the various drawers of the bureau!
 
"So!" I said—"they are uncertain of the drawer!"
 
Suddenly she desisted, looking nervously at the open windows; then, crossing the room, she drew the curtains. I crept out into the road again and by the same roundabout route came back to the empty house. Feeling my way in the darkness of the shrubbery, I found the motor bicycle which I had hidden there and I wheeled it down to the further gate of the drive and waited.
 
I could see the doctor's door, and I saw him returning along the road. As he appeared, from somewhere—-I could not determine from where—came a strange and uncanny wailing sound, a sound that chilled me like an evil omen.
 
Even as it died away, and before Dr. Stuart had reached his door I knew what it portended—that horrible wail. Some one hidden I knew not where, had warned Zara el-Khala that the doctor returned! But stay! Perhaps that some one was the dark-skinned chauffeur!
 
How I congratulated myself upon the precautions which I had taken to escape observation. Evidently the watcher had placed himself somewhere where he could command a view of the front door and the road.
 
Five minutes later the girl came............