A few minutes later a smart naval officer came on board with four men. We were soon seated in the Captain's cabin, and I rapidly gave him an outline of what had happened. His quick intelligence took in the situation at a glance. "I'll take your Mr Humber back with me," he said, "and you and your man can come along." But we were nearly to lose our man. As the officer and his men entered the engine-room Humber caught sight of them. He started, but instantly recovered himself. As the lieutenant spoke to Phail, Humber watched him closely. I saw Aubert move noiselessly but swiftly behind Humber, evidently ready for a tussle. A moment later Phail beckoned Humber to come to him. Instantly the spy's hand shot to his jacket pocket, and, as it came out, bringing with it a revolver, Aubert sprang. The next instant the revolver was on the floor and Aubert had Humber in a grip of iron. Ten minutes later, with Humber securely handcuffed, we were on our way to the destroyer, and were soon thrashing our way at top speed for home. There is little more to tell. Humber proved to be a Swede named Holmboe, and we clearly established the fact that he had been for a long time acting as the travelling agent of the Berlin espionage bureau, carrying information to Norway for transmission through the German Legation in Christiania. The conspirators in the house in Harrington Street were all taken into custody, and we soon had all the threads of their activities in our possession, including the key to the mystery of Mr Mostyn Brown, whose connection with various little affairs of espionage was clearly established. Blind Heinrich, too, was at length effectively unmasked, and, with the rest of the group, is now safely under lock and key, with ample leisure to repent of the nefarious business upon which they were engaged. On this occasion, at any rate, the secret message failed to reach Berlin, and I often laugh when I think of the amazement and anxiety that must have been caused in the enemy's camp at the sudden silence of their emissaries. To-day we can afford to make them a present of the truth! CHAPTER FOURTEEN. THE GREAT SUBMARINE PLOT. To be a success as a secret agent a wide knowledge of European hotels is an absolute necessity. You must, indeed, be familiar with the best hotel in every city of any importance, and scarcely less important is the personal acquaintance of the manager; for without his help you will inevitably find in your path a thousand difficulties, small and great, which, with his friendly assistance, melt almost insensibly away. Duty and inclination alike have led me to make a special study of hotel life, and I think I may say, without undue egotism, that there are few _maitres d'hotel_ in Europe with whom I am not on terms of acquaintance, and even in many cases warm friendship.