"Sit down. Let us talk this over," he said genially. "It was a clue worth following, wasn't it?" "Undoubtedly, sir," replied Johnson. "It was one of the few alternatives possible in such a case. I assure you, sir, I set out with high hopes." "It's a failure, Johnson, but that's no fault of yours; you did all that could be expected. I have had my rebuff, too. I have tracked the writer of the threatening letter, only to find he died two years before Monkton's disappearance. That was a nasty knock also. And yet that was a good clue too--of the two, a trifle better perhaps than yours." Detective-sergeant Johnson made no answer. Smeaton looked at him sharply. "You would say that was something to work on, wouldn't you?" Johnson reflected a moment. When you are going to exalt your own intelligence at the expense of your superior's intellect, it demands diplomacy. He spoke deferentially. "May I speak my mind plainly?" he asked. "I desire perfect frankness." Smeaton was not a little man. He knew that elderly men, in spite of their experience, grow stale, and often lose their swiftness of thought. It was well to incline their ears to the rising generation. "It was a clue worth following, sir, but personally I don't attach great importance to it." "Give me your reasons, Johnson. I know you have an analytical turn of mind. I shall be delighted to hear them." And Johnson gave his reasons. "This was a threatening letter. I daresay every big counsel receives them by the dozen. Now, let us construct for a moment the mentality of the writer; we will call him by his real name, Bolinski. A man of keen business instincts, or he would not have been the successful rogue he was. Naturally, therefore, a man of equable temperament." "It was not the letter of a man of equable temperament," interposed Smeaton grimly. "A temporary aberration," rejoined the scientific detective. "Even men of calm temperament get into uncontrollable rages occasionally. He wrote it at white heat, strung to momentary madness by the ruin that confronted him. That is understandable. What is _not_ understandable is that a man of that well-balanced mind should cherish rancour for a period of twenty-odd years." "There is something in what you say, Johnson. I confess that you are more subtle than I am." Johnson pursued his advantage. "After the lapse of twelve months, by which time he had probably found his feet again, he would recognise it, to use a phrase we both know well, sir, as `a fair cop.' He had defied the law; the law had got the better of him. He would take off his hat, and say to the law: `I give you best. You are the better man, and you won.'" Smeaton regarded his subordinate with genuine admiration. "I am not too old to learn, Johnson; you have taught me something to-night." He paused a moment, and added slowly: "You have taught me to distinguish the probable from the possible."