How he had accomplished that particular crime I did not know, but I had the best of reasons for knowing that he had left no sign of himself behind. Carefulness in covering up his traces was indeed the key-word to his criminal code, and perhaps was the secret of the success with which he had hitherto carried out his designs. Given any fresh move on his part, and some cunning scheme for obliterating the trail he had left behind--for cutting the connecting cord between the past and the present--might be looked for as surely and inevitably as night may be looked for after day. I had--more by luck than by subtlety--traced Mullen to the boatyard at Gravesend, but there I lost sight of him completely. He had taken the “Odd Trick” away with him the same evening, I was told, and had gone down the river, but what had become of him afterwards there was not the slightest evidence to show. To go down the river in search of him seemed the natural and only course, but I was beginning by this time to get some insight into my adversary’s methods, and felt that before asking myself, “Where has Mullen gone?” I should seriously consider the question, “What method has he adopted for covering up his traces?” CHAPTER XXII THE ARTFULNESS OF JAMES MULLEN “What method has Mullen adopted for covering up his traces?” I asked myself, and as I did so a passage from the letter which had been sent to him by Mrs. Burgoyne--the letter which I had fortunately intercepted--flashed into my mind. “I do not see any necessity,” she had written, “for doing as you say in regard to sending the present crew back to England under the pretence that we are not likely to be using the yacht for some time, and then, after getting the ship’s appearance altered by repainting and rechristening her the name you mention, engaging another crew of Norwegians.” If Mullen had considered it necessary to take such precautions in regard to the steam yacht, he would beyond all question consider it even more necessary to his safety that a similar course should be adopted in regard to the boat which, until opportunity came for him to leave the country, was to carry “Cæsar and his fortunes.” That boat had been described to me by Gunnell as a five-ton yawl, painted white, picked out with gold. She had by now, no doubt, been entirely metamorphosed, and before I set out to continue my search for Mullen it was of vital importance that I should know something of the appearance of the boat for which I was to look. According to the waterman Gunnell, Mullen had gone down the river when he left Gravesend that evening, and indeed it was in the highest degree unlikely that he had gone up the river towards London in a small sailing vessel. Every mile traversed in that direction would render his movements more cramped and more likely to come under observation, whereas down the river meant the open sea, with access to the entire sea-board of the country and, if necessary, of the Continent.