As he walked up from the pretty little Williston station Kennedy asked:  “One more question, Mr. Whitney.  How did Marian take the engagement?”

The district attorney hesitated.  “I will be perfectly frank, Mr. Kennedy,” he answered.  “The country-club people tell me that the girls were very cool toward each other.  That was why I got that statement from Mrs. Wainwright.  I wish to be perfectly fair to everyone concerned in this case.”

We found the coroner quite willing to talk, in spite of the fact that the hour was late.  “My friend, Mr. Whitney, here, still holds the poison theory,” began the coroner, “in spite of the fact that everything points absolutely toward asphyxiation.  If I had been able to discover the slightest trace of illuminating-gas in the room I should have pronounced it asphyxia at once.  All the symptoms accorded with it.  But the asphyxia was not caused by escaping illuminating-gas.

“There was an antique charcoal-brazier in the room, and I have ascertained that it was lighted.  Now, anything like a brazier will, unless there is proper ventilation, give rise to carbonic oxide or carbon monoxide gas, which is always present in the products of combustion, often to the extent of from five to ten per cent.  A very slight quantity of this gas, insufficient even to cause an odour in a room, will give a severe headache, and a case is recorded where a whole family in Glasgow was poisoned without knowing it by the escape of this gas.  A little over one per cent of it in the atmosphere is fatal, if breathed for any length of time.  You know, it is a product of combustion, and is very deadly—­it is the much-dreaded white damp or afterdamp of a mine explosion.

“I’m going to tell you a secret which I have not given out to the press yet.  I tried an experiment in a closed room today, lighting the brazier.  Some distance from it I placed a cat confined in a cage so it could not escape.  In an hour and a half the cat was asphyxiated.”

The coroner concluded with an air of triumph that quite squelched the district attorney.

Kennedy was all attention.  “Have you preserved samples of the blood of Mr. Templeton and Miss Wainwright?” he asked.

“Certainly.  I have them in my office.”

The coroner, who was also a local physician, led us back into his private office.

“And the cat?” added Craig.

Doctor Nott produced it in a covered basket.

Quickly Kennedy drew off a little of the blood of the cat and held it up to the light along with the human samples.  The difference was apparent.

“You see,” he explained, “carbon monoxide combines firmly with the blood, destroying the red colouring matter of the red corpuscles.  No, Doctor, I’m afraid it wasn’t carbonic oxide that killed the lovers, although it certainly killed the cat.”

Doctor Nott was crestfallen, but still unconvinced.  “If my whole medical reputation were at stake,” he repeated, “I should still be compelled to swear to asphyxia.  I’ve seen it too often, to make a mistake.  Carbonic oxide or not, Templeton and Miss Wainwright were asphyxiated.”