“My apparatus was now in full going order and there was nothing for it but to wait.  The noise in the street had subsided, but the two ruffians showed no signs of settling down.  They were now engaged in barricading the door so that it could be forced open only a few inches, thus exposing the attackers to a deadly fire.  I was much obliged to them.  Their movements would help to diffuse the gas and prevent it from settling too densely on the floor.  Also, their exertions would make them breathe more deeply and so come more rapidly under the influence of the poison.

“The time crept on; the police made no sign; the murderers rested from their labors, sometimes talking excitedly, sometimes silent for minutes at a time, and at intervals yawning like overstrung women.  And all the time the invisible stream of heavy, deadly gas was pouring out of the stovepipe and trickling unseen along the floor.  Even now it must be eddying about the murderers’ feet and slowly diffusing upwards.  If only the police would remain quiescent for an hour or two more, the danger would be over.

“The long hours of the winter’s night dragged out their weary length.  Yet not weary to me.  For, as I kept my vigil by the pipe and fed the stove silently at intervals, I was on the very tip-toe of expectation.  Every moment I dreaded to hear the disastrous crash on the door that should herald a fresh slaughter; and, as the minutes passed and all remained still, hope rose higher and higher.  Sometimes I caught a glimpse of my quarry through the chink of their cupboard door; for I had opened the slide fully a foot, finding that the clothes that hung from the pegs would screen me, even if the darkness on my side had not done so already.  So I saw one of them sit down on a low chair and crouch, shuddering, over the coke stove, while the other restlessly paced the room.

“And still the stream of deadly gas trickled unceasingly from the pipe.

“Presently the former rose and yawned heavily.  ‘Bah!’ he growled, ’I am tired.  I shall lie down.  If I fall asleep, Boris, do you watch, and wake me if you hear them coming.’

“By craning my neck through the opening I could just continue to get a glimpse of him as he threw himself on a mattress that was spread on the floor.  The other man continued for a while to pace the room; then he sat down on the chair and spread his hands out over the stove, muttering to himself.  I watched him as well as I could through the chink of the cupboard doors by the dim light of the stinking paraffin lamp; a greasy, unwholesome-looking wretch, sallow, pallid and unshorn; and thought how striking he would look in the form of a reduced, dry preparation.

“But that was impossible.  I was now working only for the police.  Regrettable as it was, I should have to surrender these two specimens to the coroner and the gravedigger.  A deplorable waste of material, but unavoidable—­even if one of them should prove to be my long-sought enemy.