"Not at all," I returned, "if there is any good reason for it." "At twelve o'clock to-night a gentleman will enter this house. If you will note him from your window I will be obliged." "To see whether he is the same one I saw last night? Certainly I will take a look, but----" "To-morrow night," he went on, imperturbably, "the test will be repeated, and I should like to have you take another look; without prejudice, madam; remember, without prejudice." "I have no prejudices----" I began. "The test may not be concluded in two nights," he proceeded, without any notice of my words. "So do not be in haste to spot your man, as the vulgar expression is. And now good-night--we shall meet again to-morrow." "Wait!" I called peremptorily, for he was on the point of closing the door. "I saw the man but faintly; it is an impression only that I received. I would not wish a man to hang through any identification I could make." "No man hangs on simple identification. We shall have to prove the crime, madam, but identification is important; even such as you can make." There was no more to be said; I uttered a calm good-night and hastened away. By a judicious use of my opportunities I had become much less ignorant on the all-important topic than when I entered the house. It was half past eleven when I returned home, a late hour for me to enter my respectable front door alone. But circumstances had warranted my escapade, and it was with quite an easy conscience and a cheerful sense of accomplishment that I went up to my room and prepared to sit out the half hour before midnight. I am a comfortable sort of person when alone, and found no difficulty in passing this time profitably. Being very orderly, as you must have remarked, I have everything at hand for making myself a cup of tea at any time of day or night; so feeling some need of refreshment, I set out the little table I reserve for such purposes and made the tea and sat down to sip it. While doing so, I turned over the subject occupying my mind, and endeavored to reconcile the story told by the clock with my preconceived theory of this murder; but no reconcilement was possible. The woman had been killed at twelve, and the clock had fallen at five. How could the two be made to agree, and which, since agreement was impossible, should be made to give way, the theory or the testimony of the clock? Both seemed incontrovertible, and yet one must be false. Which?