“One of them.  She had tried them all, poor, silly girl!  You must understand that for a habitual drug-taker suddenly to be deprived of drugs would lead to complete collapse, perhaps death.  And during the last few days I had noticed a peculiar nervous symptom in Rita Irvin which had interested me.  Finally, the day before yesterday, she confessed that her usual source of supply had been closed to her.  Her words were very vague, but I gathered that some form of coercion was being employed.”

“With what object?”

“I have no idea.  But she used the words, ‘They will drive me mad,’ and seemed to be in a dangerously nervous condition.  She said that she was going to make a final attempt to obtain a supply of the poison which had become indispensable to her.  ‘I cannot do without it!’ she said.  ‘But if they refuse, will you give me some?’”

“What did you say?”

“I begged of her, as I had done on many previous occasions, to place herself in my hands.  But she evaded a direct answer, as is the way of one addicted to this vice.  ‘If I cannot get some by tomorrow,’ she said, ‘I shall go mad, or dead.  Can I rely on you?’”

“I told her that I would prescribe cocaine for her on the distinct understanding that from the first dose she was to place herself under my care for a cure.”

“She agreed?”

“She agreed.  Yesterday afternoon, while I was away at an important case, she came here.  Poor Rita!” Margaret’s soft voice trembled.  “Look —­she left this note.”

From a letter-rack she took a square sheet of paper and handed it to the Chief Inspector.  He bent his fierce eyes upon the writing—­large, irregular and shaky.

“‘Dear Margaret,’” he read aloud. “’Why aren’t you at home?  I am wild with pain, and feel I am going mad.  Come to me directly you return, and bring enough to keep me alive.  I—­’, Hullo! there’s no finish!”

He glanced up from the page.  Margaret Halley’s eyes were dim.

“She despaired of my coming and went to Kazmah,” she said.  “Can you doubt that that was what she went for?”

“No!” snapped Kerry savagely, “I can’t.  But do you mean to tell me, Miss Halley, that Mrs. Irvin couldn’t get cocaine anywhere else?  I know for a fact that it’s smuggled in regularly, and there’s more than one receiver.”

Margaret looked at him strangely.

“I know it, too, Inspector,” she said quietly.  “Owing to the lack of enterprise on the part of our British drug-houses, even reputable chemists are sometimes dependent upon illicit stock from Japan and America.  But do you know that the price of these smuggled drugs has latterly become so high as to be prohibitive in many cases?”

“I don’t.  What are you driving at, miss?”

“At this:  Somebody had made a corner in contraband drugs.  The most wicked syndicate that ever was formed has got control of the lives of, it may be, thousands of drug-slaves!”