The Professor had never shirked danger throughout the whole course of his career. And in this case, as he reflected, he already stood in such imminent danger that his present actions could hardly increase it. If his theory were correct, a determined and unknown assassin held in his hand already the weapon which was aimed against his life. Why had he not struck, months ago, when the Professor was in blissful ignorance that his life was threatened? This was one of the aspects of a case which, in spite of the perils which it held for himself, thrilled him as no case had ever thrilled him before. Sitting here, contemplating the peaceful afternoon, the Professor reviewed his theory for the last time, testing it with all the apparatus of probability. It _must_ be correct, there was no other theory which would fit in with all the data before him. Yet, how could it be correct, in the face of the formidable array of facts which seemed to disprove it? This seeming contradiction it must be his task to unravel, and that alone. For he had realized at once that it was no good calling in the aid of the police, even of Hanslet, whose experience had taught him that the Professor’s most extraordinary statements had a way of justifying themselves. The police would merely confront him with their so-called facts, and seek to prove to him that his theory was utterly untenable. He could give them nothing tangible to go upon, could give them no clue which would lead to the capture of the undetected criminal he knew to be at large. Even if they accepted his theory in its entirety, how could they protect him from the dangers which encompassed him? Sooner or later, in some unguarded moment, the shadow would leap out upon him, and the Professor’s theory would be proved upon his own body. No, physical precautions were useless. It must be a battle of wits between them—himself and this mysterious killer. How far had a watch been kept upon his own actions, the Professor wondered? He was almost certain that he had not been followed to Corfe Castle, but he was by no means so certain that his pretended departure from England had imposed upon his adversary. _The Times_ of Friday had contained the paragraph mentioning his visit to Australia. So far, so good. But it was almost with surprise that he had failed to find the message in the personal column, which should inform him that the letter which he daily expected had arrived. The Professor rose to his feet, and walked slowly back to the inn. He had ordered dinner at seven o’clock, and it was already past six. The landlord was standing at the door, and the Professor nodded pleasantly to him as he entered. “What a beautiful afternoon!” he said. “I have been admiring the view from the Castle. A very fine prospect indeed, is it not?” “Well, sir, some admires it and some don’t,” replied the landlord. “I fancies something with a bit more life in it myself. But I dessay it’s a change to you after London.”