"That made matters comparatively easy," continued Malcolm Sage. "The outrages were clearly not acts of revenge upon any particular person; for they involved nine different owners. They were obviously the work of someone subject to a mania, or obsession, which gripped him when the moon was at the full." "But how did you fix the actual spot?" burst out Inspector Wensdale excitedly. "Each of the previous acts had been either in a diametrically opposite direction from that immediately preceding it, or practically on the same spot. For instance, the first three were north, east, and south of Hempdon, in the order named. Then the cunning of the perpetrator prompted him to commit a fourth, not to the west; but to the south, within a few yards of the previous act. The criminal argued, probably subconsciously, that he would be expected to complete the square." "But what made you fix on Hempdon as the headquarters of the blackguard?" enquired Sir John. "That was easy," remarked Malcolm Sage, polishing the thumb-nail of his left hand upon the palm of his right. "Easy!" The exclamation burst involuntarily from the inspector. "You supplied me with a large scale-map showing the exact spot where each of the previous maimings had taken place. I drew a square to embrace the whole. Lines drawn diagonally from corner to corner gave me the centre of gravity." "But----" began the inspector. Ignoring the interruption Malcolm Sage continued. "A man committing a series of crimes from a given spot was bound to spread his operations over a fairly wide area in order to minimise the chance of discovery. The longer the period and the larger the number of comes, the greater the chance of his being located somewhere near the centre of his activities." "Well, I'm damned!" remarked Sir John for the second time. Then suddenly turning to Inspector Wensdale, "Dammit!" he exploded, "why didn't you think of that?" "There was, of course, the chance of his striking in another direction," continued Malcolm Sage, digging into the bowl of his pipe with a penknife, "so I placed the men in such a way that if he did so he was bound to be seen." Inspector Wensdale continued to gaze at him, eager to hear more. "But what was that you said about race-memory?" Sir John had quieted down considerably since Malcolm Sage had begun his explanation. "I should describe it as a harking back to an earlier phase. It is to the mind what atavism is to the body. In breeding, for instance"--Malcolm Sage looked across to Sir John--"you find that an offspring will manifest characteristics, or a taint, that is not to be found in either sire or dam." Sir John nodded. "Well, race-memory is the same thing in regard to the mental plane, a sort of subconscious wave of reminiscence. In Callice's case it was in all probability the memory of some sacrificial rite of his ancestors centuries ago." "A case of heredity."