"Oh, it is easy enough to imagine motives, although I do not guarantee having hit on the right one. But what do you think of this for a guess? Miss Derwent, who knows that her brother may any day be in need of a hiding-place, has given him the key to their back door. Coming to town, she meets Greywood, dines with him, and invites him to spend the evening with her (having some reason for supposing that her brother is safely out of the way). During this visit they have a violent quarrel, and, in the midst of it, young Derwent, who has come in through the kitchen, suddenly appears. Let us also presume that he is intoxicated. He discovers his sister alone with a man, who is unknown to him, and with whom she is engaged in a bitter dispute. The instinct to protect her rises within him. His eyes fall on a weapon, lying, let us suppose, on the parlour table. He seizes it, and in his drunken rage, staggers across the room and plunges it into Greywood's heart. What girl could be placed in a more terrible position? She is naturally forced to shield her brother. So she hits on a plan for diverting suspicion from him, which would have been successful, if Fate had not intervened in the most extraordinary way. You remember, that it came out that on Wednesday she went in and out of the building very frequently. During one of these many comings and goings, she manages to extract the key of the vacant apartment, to have it copied, and to return it without its absence being noticed. They then wait till the early hours of the morning before venturing to move the body, which they carry to the place where it was found. Unfortunately for them, they locked the dead man in, and in this way rendered their detection much more easy. For it limited the number of suspected persons to three--to the three people, in fact, who could have had the key in their possession, even for a short time. On returning to their own rooms, they discover that they have lost something of great importance. The young man searches for it long and vigorously. He does not find it----" "How do you know he didn't find it?" I interrupted. "Because _I_ found it," asserted the detective triumphantly. "Indeed! And what was it?" "The handle--or, to be more accurate, the head--of the fatal weapon." "Really!" I exclaimed; "you found it? Where?" "It had fallen in between the dead man's trousers and the folds of his shirt." "It must be pretty small, then." "It is. Look at it," and he laid on the table a jewelled dagger-hilt about an inch and a half long. "That!" I exclaimed contemptuously; "why, that is nothing but a toy." "Not a toy," replied Mr. Merritt, "but an ornament. A useful ornament; for it is the head of one of those jewelled hat-pins that have been so fashionable of late. A dagger with the hilt encrusted with precious stones is quite a common design." "Did you find the pin itself?" I asked. "No, I did not," the detective answered regretfully.