We had been summoned over the telephone to the Blake mansion by Reginald Blake, Mrs. Blake’s eldest son.  Reginald had been very reticent over the reason, but had seemed very anxious and insistent that Kennedy should come immediately.

Craig read quickly and I followed him, fascinated by the letter from its very opening paragraph.

“Dear Madam,” it began.  “Having received my diploma as doctor of medicine and bacteriology at Heidelberg in 1909, I came to the United States to study a most serious disease which is prevalent in several of the western mountain states.”

So far, I reflected, it looked like an ordinary appeal for aid.  The next words, however, were queer:  “I have four hundred persons of wealth on my list.  Your name was—­”

Kennedy turned the page.  On the next leaf of the letter sheet was pasted a strip of gelatine.  The first page had adhered slightly to the gelatine.

“Chosen by fate,” went on the sentence ominously.

“By opening this letter,” I read, “you have liberated millions of the virulent bacteria of this disease.  Without a doubt you are infected by this time, for no human body is impervious to them, and up to the present only one in one hundred has fully recovered after going through all its stages.”

I gasped.  The gelatine had evidently been arranged so that when the two sheets were pulled apart, the germs would be thrown into the air about the person opening the letter.  It was a very ingenious device.

The letter continued, “I am happy to say, however, that I have a prophylactic which will destroy any number of these germs if used up to the ninth day.  It is necessary only that you should place five thousand dollars in an envelope and leave it for me to be called for at the desk of the Prince Henry Hotel.  When the messenger delivers the money to me, the prophylactic will be sent immediately.

“First of all, take a match and burn this letter to avoid spreading the disease.  Then change your clothes and burn the old ones.  Enclosed you will find in a germ-proof envelope an exact copy of this letter.  The room should then be thoroughly fumigated.  Do not come into close contact with anyone near and dear to you until you have used the prophylactic.  Tell no one.  In case you do, the prophylactic will not be sent under any circumstances.  Very truly yours, Dr. Hans Hopf.”

“Blackmail!” exclaimed Kennedy, looking intently again at the gelatine on the second page, as I involuntarily backed away and held my breath.

“Yes, I know,” responded Mrs. Blake anxiously, “but is it true?”

There could be no doubt from the tone of her voice that she more than half believed that it was true.

“I cannot say—­yet,” replied Craig, still cautiously scanning the apparently innocent piece of gelatine on the original letter which Mrs. Blake had not destroyed.  “I shall have to keep it and examine it.”