When she was out of sight, he went swiftly back, and, crossing the hall, entered the drawing-room. He turned on all the lights and stood for one moment, taking stock of the room generally, and then slowly approached the window. No marks were discernible on the carpet, but a search revealed little pieces of dry earth on the stained wood. Carefully he unbarred the shutters, taking great pains not to touch anything but the bottom of the bolt, and the extreme rim of the shutters; there was no longer uncertainty about the entrance. Pieces of earth lay on the sill, only minute particles as if it had been hastily swept, but the white paint was scored to the left of the centre with a number of tiny criss-cross scratches, and among them dirt was ground in. Some one’s boot had been pressed and then turned upon it, it was impossible to doubt it. If confirmation were needed, it was given by the damning evidence of the faint imprint of finger-tips on the lintel, where any one entering by the window would naturally have caught hold to steady himself. As he gazed, Humblethorne let out his breath in a long “ah!” Suddenly, with that agility of performance with which the mind sometimes chooses to delight those who have long been turning over a set of isolated facts without being able to fit them together, he saw clear: three facts came together without conscious effort and made a pattern. The mouth of which Lady Penterton’s had reminded him in vain was that of the unsociable stranger at the Rose and Crown, he remembered it now perfectly, and had no doubt whatever—fact number one; that stranger had gone out and returned hurriedly to the inn shortly after midnight on the night of the murder—fact number two; some one had made a secret entrance into the Towers—fact number three. In a flash his mind had forged a complete chain of events: the stranger was the son of whom he had been hearing; he had returned home secretly—for what purpose was at the moment immaterial—he had encountered his father, whether by arrangement or by accident; a quarrel had ensued; the son had struck his father down, and fled—and some one had first let him in, and had afterwards closed the window and bolted the shutters behind him. Here the shutters did not help him; no finger prints were discernible. Closing them again, he sat down and ran over in his mind all the evidence in the light of what he now suspected with such deadly confidence. It remained to track and identify the stranger of the inn, perhaps a difficult but at any rate a straightforward task, and to investigate further such questions as Castle’s property in shoes. He rose up, full of energy and certain of success, went into the hall and rang the bell. When Fairlie presented himself he said in a casual manner, “Oh, Fairlie, do you know where Mr. Castle is?” “He was resting, but I think I heard him come down a few minutes ago and go into his study. Do you wish to speak to him?”