I took my way up the back of the hill and stole through the wood, carefully keeping a watchful look out all round me, for I feared the presence of either of the sets of spies. At the very top I came upon a good sized circle of masonry, low but heavily built of massive stones completely covered with rich green lichen. The circle was some fifteen feet diameter, and the top was slightly arched as though forming a roof. Leaning over it I could hear a faint trickle of water; this was evidently the source of the castle supply. I walked round it, examining it carefully; anything which had any direct communication with the castle was at present of possibly the supremest importance. There was no flaw or opening anywhere; and from the unbroken covering of the stones by the lichen, it was apparent that there had been no disturbance for years. I sat down on the edge of the stonework and for a long time thought over matters of probability. If underneath me, as was almost to be taken for granted, lay the reservoir of the castle, it must have been made coevally with Crom itself, or even with the older castle on whose ruins it was built. It must be fed by springs in the rock which formed the base of the hill and cropped out all over it; and if it was not approachable from without, there must be some way of reaching the water from within. It might be that the chamber which contained the reservoir had some other entrance from the hill top, or from some lower level. Accordingly I made as I conceived a bee line for the castle, till I came to the very base of the hill, for I knew that in matters of water conduit the direct way is always chosen where work has to be done. As I went, I conned the ground carefully; not merely the surface for that was an uniform thick coating of brown pine needles, but the general conformation. Where a trench has been made, there is ever after some trace of it to be found. Even if the workmen level the trench most carefully there and then, the percolation of rain through the softer broken earth will make discovery of the change by shrinkage. Here, however, there was no such sign; the ground, so far as one could judge, had never been opened. The trees grew irregularly, and there was no gap such as would be, had one ever been removed. Here and there particles of rock cropped out amongst the pine needles just as anywhere else. If any opening existed it was not on the direct line between the reservoir and the castle. Back again I went to the reservoir, and, using it as a base, began to cast around for some opening or sign. I made circles in all directions, just as a retriever does when looking for a fallen partridge in a dry stubble when the scent is killed by heat.