As a thief in the night

by R. Austin Freeman

“This brings us to the end of the first stage; the conclusions arrived at by a careful study of the depositions. But following hard on the inquest was your visit to me when you gave me the particulars of your past life and your relations with Barbara and Monkhouse. Now your little autobiographical sketch was extremely enlightening, and, as it has turned out, of vital importance. In the first place, it made clear to me that your relations with Barbara were much more intimate than I had supposed. You were not merely friends of long standing; you were virtually in the relation of brother and sister. But with this very important difference: that you were not brother and sister. An adopted brother is a possible husband; an adopted sister is a possible wife. And when I considered your departure to Canada with the intention of remaining there for life, and your unexpected return, I found that the bare possibility that Barbara might wish to be released from her marriage had acquired a certain measure of probability.

“But further; your narrative brought into view another person who had died. And the death of that person presented a certain analogy with the death of Monkhouse. For if Barbara had wished to be your wife, both these persons stood immovably in the way of her wishes. Of course there was no evidence that she had any such wish, and the death of Stella was alleged to have been due to natural causes. Nevertheless, the faint, hypothetical suggestions offered by these new facts were strikingly similar to those offered by the previous facts.

“The next stage opened when I read your diary, especially the volume written during the last year of Stella’s life. But now one came out of the region of mere speculative hypothesis into that of very definite suspicion. I had not read very far when, from your chance references to the symptoms of Stella’s illness, I came to the decided conclusion that, possibly mingled with the symptoms of real disease, were those of more or less chronic arsenical poisoning. And what was even more impressive, those symptoms seemed to be closely comparable with Monkhouse’s symptoms, particularly in the suggestion of a mixed poisoning partly due to minute doses of arsine. I need not go into details, but you will remember that you make occasional references to slight attacks of jaundice (which is very characteristic of arsine poisoning) and to ‘eye-strain’ which the spectacles failed to relieve. But redness, smarting and watering of the eyes is an almost constant symptom of chronic arsenic poisoning. And there were various other symptoms of a decidedly suspicious character to which you refer and which I need not go into now.

“Then a careful study of the diary brought into view another very impressive fact. There were considerable fluctuations in Stella’s condition. Sometimes she appeared to be so far improving as to lead you to some hopes of her actual recovery. Then there would be a rather sudden change for the worse and she would lose more than she had gained. Now, at this time Barbara had already become connected with the political movement which periodically called her away from home for periods varying from one to four weeks; and when I drew up a table of the dates of her departures and returns, I found that the periods included between them—that is the periods during which she was absent from home—coincided most singularly with Stella’s relapses. The coincidence was so complete that, when I had set the data out in a pair of diagrams in the form of graphs, the resemblance of the two diagrams was most striking. I will show you the diagrams presently.

“But there was something else that I was on the lookout for in the diary, but it was only quite near the end that I found it. Quite early, I learned that Stella was accustomed to read and work at night by the light of a candle. But I could not discover what sort of candle she used; whether it was an ordinary household candle or one of some special kind. At last I came on the entry in which you describe the making of the wax mould; and then I had the information that I had been looking for. In that entry you mention that you began by lifting the reflector off the candle, by which I learned that the receptacle used was not an ordinary candlestick. Then you remark that the candle was of ‘good hard wax’; by which I learned that it was not an ordinary household candle—these being usually composed of a rather soft paraffin wax. Apparently, it was a stearine candle such as is made for use in candle-lamps.”

“But,” I expostulated, “how could it possibly matter what sort of candle she used? The point seems to be quite irrelevant.”

“The point,” he replied, “was not only relevant; it was of crucial importance. But I had better explain. When I was considering the circumstances surrounding the poisoning of Monkhouse, I decided that the probabilities pointed to Barbara as the poisoner. But she was a hundred miles away when the poisoning occurred; hence the question that I asked myself was this: Was there any method that was possible and practicable in the existing circumstances by which Barbara could have arranged that the poisoning could be effected during her absence? And the answer was that there was such a method, but only one. The food and the medicine were prepared and administered by those who were on the spot. But the candles were supplied by Barbara and by her put into the bedside candle-box before she went away. And they would operate during her absence.”

“But,” I exclaimed, “do I understand you to suggest that it is possible to administer poison by means of a candle?”

“Certainly,” he replied. “It is quite possible and quite practicable. If a candle is charged with finely powdered arsenious acid—‘white arsenic’—when that candle is burnt, the arsenious acid will be partly vaporized and partly converted into arsine, or arseniureted hydrogen. Most of the arsine will be burnt in the flame and reconverted into arsenious acid, which will float in the air, as it condenses, in the form of an almost invisible white cloud. The actual result will be that the air in the neighbourhood of the candle will contain small traces of arsine—which is an intensely poisonous gas—and considerable quantities of arsenious acid, floating about in the form of infinitely minute crystals. This impalpable dust will be breathed into the lungs of any person near the candle and will settle on the skin, from which it will be readily absorbed into the blood and produce all the poisonous effects of arsenic.

“Now, in the case of Harold Monkhouse, not only was there a special kind of candle, supplied by the suspected person, but, as I have told you, the symptoms during life and the appearances of the dead body, all seemed to me to point to some method of poisoning through the lungs and skin rather than by way of the stomach, and also suggested a mixed poisoning in which arsine played some part. So that the candle was not only a possible medium of the poisoning; it was by far the most probable.