"As I was already drenched to the skin this mattered little, and, notwithstanding my condition, a thrill of gratification warmed me on finding the door to be merely latched. Just as a party of six which had been scouring the east valley appeared upon the opposite bank I entered, and shut the door behind me."
"Well--what then?"
"I went up to the room overlooking the laboratory--for, although no one seems to have attached any particular importance to the circumstance, from the window of this room you could, if the laboratory window were bigger, easily spring through."
"And what did you find there?"
"The origin of the mysterious light."
"Which was?"
"A match! Now, you will agree with me that green spiders do not use matches. Inference: That some human being had been in the room on the night of the murder, and had struck a match, which had been observed by Jamieson. There were also certain marks which considerably mystified me at first. On the thick grime of the window-ledge--inside--it was evident that a board had rested. That is to say, a board had been, for some reason, placed across the room. The mortar had fallen off the wall in one corner, and here I found on the floor an impression as though a box had stood on end there--evidently to support the other extremity of the board.
My next discovery was even more interesting. I found traces of finger-marks--which, by the way, I removed before leaving--on the sill and around the inside of the window-frame. Someone had come in by the window!"
"But I remembered that, until I opened it to investigate, the window had been closed. Therefore the mysterious visitor had closed it behind him. Since his bloodstained finger marks testified to the state of his hands on entering, how had he opened the window from outside--a somewhat difficult operation--and yet left no traces upon the sash? For there were none. I assumed, by way of argument, that he had opened the window from the inside."
"I had now constructed a hypothetical assassin who had got into the end house in Spindle Lane, entered the bacteriological laboratory, murdered the Professor, returned through the window, and struck a match--for there were traces of blood upon it. Why had he come back to the room, and by what means had he reached the window of the laboratory? It was upon subsequently examining the laboratory (for the local officer in charge, being an acquaintance, raised no objection to my doing so) that two points became clear. First: That the window could never have been opened from outside. Second: The probability that a plank had been placed across--the same plank that had been used for some other mysterious purpose!"
"Working, then, upon this theory, it immediately became evident that a plank could only have been placed in position from one of the windows. Here I had an enlightening inspiration. My assassin must have entered the house from the riverside, as I had done! How had he conveyed the plank into the place? A boat! You will mark that this was all pure supposition. Nevertheless, I determined, for the moment, to assume that a plank had been used."
"It was with this idea before me that I made my examination of the laboratory, and the various facts, viewed in this new light, began to assume their proper places. The horrible marks, suggestive of an incredible assailant, which so horrified us when we first observed them, were less inexplicable when regarded as intentional and not accidental! To consider the handmark upon the ceiling, for example, as incidental to a struggle for life, pointed to an opponent possessing attributes usually associated with insects; but it was the easiest thing in the world for a tall man, standing upon a table, to imprint such a mark! This startling revelation, taken in conjunction with the locked door and the impossibility of anyone entering the place from the quadrangle, brought me face to face with a plausible solution of the mystery."
"The elaborate nature of the affair pointed to premeditation, and the fact that the missing man had locked the door was most significant. Who could have known that he would be there upon this particular night, and why had he failed to unlock the door? For you will remember that the key was in the lock. Then, again, how did it come about that his cries for assistance did not arouse the people living in Spindle Lane?"
"These ideas carried me to the second stage of my theory, and I assumed that a plank had been placed in position for the purpose of exit from, and not of entrance to, the laboratory! My final conclusion was as follows."
"Professor Brayme-Skepley entered the end house in Spindle Lane from a boat--which he obtained at Long's boathouse--bearing a plank and some kind of box or case. The plank he placed from window to window, the case upon the floor of the house in the Lane. He then returned to his boat, and landed beside the house.
Entering the quadrangle, as we know, he went into the laboratory, and locked the door. His next proceeding was to smash everything breakable, wrench the window from its fastenings, and imprint the weird tracks and marks which proved so misleading. The book beneath the skylight and the lancet in the woodwork were the artistic touches of a man of genius. By this time it was close upon one o'clock, and, desirous of ascertaining whether his apparatus for bringing about the spider illusion was ready for instant use, he crawled from window to window. It was his match that Jamieson saw from the lodge door, and had Jamieson been a man of mettle the whole plot must have failed."
"He then, probably, grew very impatient whilst awaiting the coming of Jamieson, but he heard him ultimately, and lay in the light of the lamps as we have heard. All fell out as he had planned. Jamieson climbed on to the dust-box and looked into the laboratory; then he ran for the window ladder, as a reasoning mind would have easily foreseen he would do. The Professor, during his absence, broke the lamps, climbed along his plank, and pulled it after him."
I had listened with breathless interest so far, but I now broke in: "How about the spider?"
"Perfectly simple!" answered Harborne. "Allow me."
He reached down for the leather case and unstrapped it. From within he took... a magic lantern!
"What!" I exclaimed. "A magic lantern?"
"With cinematograph attachment! Here, you see, is the film--not improved by having been in the river. Some kind of South American spider, is it not? Beautifully coloured and on a black ground. The plank, supported upon the window-ledge and the upturned case, did duty for a table, and as Jamieson went up the ladder, and surveyed the place from the south-east, this was directed from the window of the end house across the few intervening yards of Spindle Lane and through the pen laboratory window on to the north-west corner of the wall."
"The beam from the lens would be hidden by the partition and only the weird image visible from the porter's point of view--though had he mounted further up the ladder and glanced over the wall he must have observed the ray of light across the lane. The familiar illuminated circle, usually associated with such demonstrations, was ingeniously eliminated by having a transparent photograph on an opaque ground. The Professor then retreated to the back door and hauled up his boat by the painter--which he would, of course, have attached there. He pulled upstream to return his boat and to sink his apparatus. He was probably already disguised--his fur coat would have concealed this from Jamieson."
I stared at Harborne in very considerable amazement.
"You are apparently surprised," he said with a smile; "but there is really nothing very remarkable in it all. I have not bored you with all the little details that led to the conclusion, nor related how I suffered a second ducking in leaving the end house; but my solution was no more than a plausible hypothesis until a happy inspiration, born of nothing more palpable than my own imaginings, led me to search for and find the cinematograph. You are about to ask where I found it: I answer, in the deep hole above Long's boat-house where Jimmy Baker made his big catch last summer. Brayme-Skepley, being a man of very high reasoning powers, would, I argued, deposit it up and not downstream, knowing that the river would be dragged. He would furthermore put it in the hole, so that the current should not carry it below college."