With this information and a very meagre report of the Wainwright trip to the Far East, which had taken in some out-of-the-way places apparently, I hastened back to Kennedy.  He was surrounded by bottles, tubes, jars, retorts, Bunsen burners, everything in the science and art of chemistry, I thought.

I didn’t like the way he looked.  His hand was unsteady, and his eyes looked badly, but he seemed quite put out when I suggested that he was working too hard over the case.  I was worried about him, but rather than say anything to offend him I left him for the rest of the afternoon, only dropping in before dinner to make sure that he would not forget to eat something.  He was then completing his preparations for the evening.  They were of the simplest kind, apparently.  In fact, all I could see was an apparatus which consisted of a rubber funnel, inverted and attached to a rubber tube which led in turn into a jar about a quarter full of water.  Through the stopper of the jar another tube led to a tank of oxygen.

There were several jars of various liquids on the table and a number of chemicals.  Among other things was a sort of gourd, encrusted with a black substance, and in a corner was a box from which sounds issued as if it contained something alive.

I did not trouble Kennedy with questions, for I was only too glad when he consented to take a brisk walk and join me in a thick porterhouse.

It was a large party that gathered in Kennedy’s laboratory that night, one of the largest he had ever had.  Mr. and Mrs. Wainwright and Miss Marian came, the ladies heavily veiled.  Doctor Nott and Mr. Whitney were among the first to arrive.  Later came Mr. Vanderdyke and last of all Mrs. Ralston with Inspector O’Connor.  Altogether it was an unwilling party.

“I shall begin,” said Kennedy, “by going over, briefly, the facts in this case.”

Tersely he summarised it, to my surprise laying great stress on the proof that the couple had been asphyxiated.

“But it was no ordinary asphyxiation,” he continued.  “We have to deal in this case with a poison which is apparently among the most subtle known.  A particle of matter so minute as to be hardly distinguishable by the naked eye, on the point of a needle or a lancet, a prick of the skin scarcely felt under any circumstances and which would pass quite unheeded if the attention were otherwise engaged, and not all the power in the world—­unless one was fully prepared—­could save the life of the person in whose skin the puncture had been made.”

Craig paused a moment, but no one showed any evidence of being more than ordinarily impressed.

“This poison, I find, acts on the so-called endplates of the muscles and nerves.  It produces complete paralysis, but not loss of consciousness, sensation, circulation, or respiration until the end approaches.  It seems to be one of the most powerful sedatives I have ever heard of.  When introduced in even a minute quantity it produces death finally by asphyxiation—­by paralysing the muscles of respiration.  This asphyxia is what so puzzled the coroner.