The wick smouldered and glowed, and began to creep towards the string, which crossed the stock of the pistol about three inches from the burning end. Colwyn took out his watch and timed its progress. In four minutes the first inch of the wick was consumed, and the spark at the end continued to creep sullenly forward in a dull red glow. In another eight minutes it reached the string, and Colwyn eagerly watched the process of the burning of the binding. The string singed, smouldered, and when nearly severed, sprang apart under the pressure of the hammer and trigger it had been holding back. The released hammer fell with full force on the cap on the nipple, and exploded it. There, then, seemed the explanation. Mrs. Heredith had been shot with Nepcote's revolver, but it was not the deliberately deadened sound of that slight weapon which had startled the guests in the dining-room on the night of the murder. The report they had heard was made by the heavier pistol in front of him. It was a ruse of terrifying simplicity but diabolical ingenuity. The wick of the tinder-lighter was an admirable slow match, obtainable in any tobacconist's shop for a few pence, which, by means of this trick, had established a false alibi for the actual murderer by causing the report which had reached the dining-room, and sent the inmates hastening upstairs to ascertain the cause. The shot which had mortally wounded Mrs. Heredith must have been fired before. How long before? Obviously not very long. That would have been dangerous to the murderer's plans. He had to consider two things. There was the chance of somebody entering the room before the false charge exploded, and the possibility that the coldness of the body of his victim might arouse medical suspicions. Colwyn did not think that the criminal had avoided killing Mrs. Heredith so as to ensure against that risk of discovery. The infliction of a mortal wound which failed to cause immediate death not only required a high degree of anatomical knowledge, but left the door open to a dying confession which might have upset the whole plan. Fate had helped the murderer to that extent. But the murderer owed more than that to Fate. It was to that grim goddess he was indebted for the last wonderful touch of actuality which lifted the whole contrivance so superbly above the realm of artifice. Suspicion was in the last degree unlikely in any case, but Hazel Rath's entry and loud scream, just before the moment fixed for the explosion, ensured complete success by adding a natural verisimilitude which might have deceived the very Spirit of Truth. Colwyn esteemed himself fortunate indeed in lighting on what he believed to be the facts. Who could have imagined a situation in which whimsical Destiny had ironically stooped down from her high place to dabble ignobly in a murderer's ghastly plot?