“I sent her to police headquarters.”

“And is that all?”

“Mr. Folett telegraphed that he would be here at ten.”

“It’s after that now—­it’s nearly noon.  You can go to lunch if you wish.  There’s the door—­ Hullo, it’s Mr. Folett now.  Be back in an hour.”

“Yes, Uncle Adam,” answered the girl.  She always called him uncle, since he had taken such an interest in her.  She went out as the caller entered, and left the two men talking over a business matter which has nothing to do with our story.

It was two o’clock before Adam Adams found himself free once more.  He procured a lunch and then took a subway train halfway uptown.  He walked two blocks westward and ascended the steps of a fine brown-stone residence.  He asked for Doctor Calkey and was ushered into a private den, where the doctor, a tall, spare man of sixty, soon joined him.

“My good friend Adams!” cried the doctor, shaking hands warmly.  “Where have you kept yourself?  Surely you have not been to see me for a year, or is it longer?  I have missed you so much—­and the comforting smokes we had together?  Why did you desert me?  You knew I could not come to you—­that I never go out.  And you do not bring any business to me—­”

“I had none to bring, and I have been very busy.  But I have missed our meetings, I must confess.”

“Ah, I am glad to learn I was not entirely forgotten.  And you have been busy, and still nothing for Rudolph Calkey to do, nothing to analyze, nothing to dissect—­”

“I’ve got a knot now for you.”

“Good! good!  I trust it is a good complication—­I love them so—­there is such a satisfaction when the end is reached.  But not yet—­no, not yet.  A glass of wine first—­something prime—­I imported it myself, so that I would know what I am getting.”

The wine was soon forthcoming and then a cigar for the detective and a pipe for the doctor.  At last the latter threw himself into an old easy chair and gazed at his caller expectantly.

“I am ready to untie the knot,” he said.  “What is it?”

CHAPTER X

AN AFFAIR OF THE HEART

There was a moment of silence.

“Briefly put, doctor, the case is this,” said Adam Adams.  “I want to know if there is anything known to the medical world, a powder or something of that sort, strong enough to kill a person if he should breathe of it.”

“A powder strong enough to kill a person?” The brow of the old physician contracted.  “It would have to be very powerful to do that.  You mean if a person was boxed up with it—­like one killed by gas?”

“No, not at all.  I mean a powder that could be held to a person’s nose and mouth in the open, when it would make that person sick and give him cramps perhaps.”

“And kill him?”

“Yes.”

The old doctor rubbed his hands in thought.  “That is a subject for speculation.  Certain cyanide compounds might be powerful enough to do so under certain conditions.  Any real dry powder would choke a person if he got a big dose of it.  I heard of a boy who came near dying as the result of breathing in a quantity of extra dry licorice powder.  But he was smothered and did not have cramps.”