"It pays me to be so. I repeat, my reputation is at stake. I have arrested a man for murder, and I am bound to prove him guilty. There are jealousies in all professions; there are jealousies in mine. I am surrounded by men who envy me, and who would like to step in my shoes. They would clap their hands in delight if I let the man I arrested slip through my fingers. Well, I don't intend to give them this satisfaction. My present visit to you is partly private, partly professional. Of course, if you say to me, 'Mr. Lambert, I decline to have anything to do with your private feelings,' the only thing open to me would be to keep those private feelings to myself, and to treat you, professionally, as a witness who was not disposed to assist me." "Justice must not be thwarted," he said. "Exactly. You hit the nail on the head. May we continue the conversation on the lines that will suit you?" "Well, continue," he said; "it is rather novel to me, and I will endeavour to work up an interest in a matter so entirely foreign to me. You see," he added, and I was not sure whether he intended to be humorous or serious, "there is nothing scientific in it." "Not in a strict sense, perhaps, but, allowing a latitude, there is something scientific in the methods we detectives pursue. The piecing together of the loose bits of evidence which we hunt up, a bit here, a bit there, arguing upon it, drawing conclusions from it, rejecting what will not fit, filling up the empty spaces, until we present the whole case without a crack in it for a guilty man to slip through--that is what we call circumstantial evidence, and it is really a science, doctor. Where did we break off? I was contending that it would have been wrong for you to have left the Court without speaking of the startling resemblance between Mr. Reginald Boyd and the man you saw coming from his father's house in the middle of the night. It would have been worse than wrong, it would have been criminal. Now, doctor, a man of your penetration could not be mistaken. He says he was home and in bed at the time, but it is impossible for him to prove it. And why? Because there is not a shadow of doubt that he was the man you saw. There must be no wavering in your evidence on this point; the crime must be brought home to him; he must not escape. Doctor Pye, you must let no feeling of compassion prevent you from stating the honest truth. You see what is at stake in this matter." I may say, without vanity, that I was playing my cards well, and if I did not laugh in his face--which would have been foolish, though I could have done so with much enjoyment--I am entitled to my laugh at the recollection of the scene. "Your reputation is at stake," he said. "I don't deny it; and the ends of justice; a much more important thing to a gentleman of your position." "Am I to infer that my presence will be necessary in a criminal court?"