It occurred to Burton that the men might leave the cycles and approach on foot, so he closely scrutinised all the passengers of foreign appearance who passed on the way to the boat. None of them answered to Micklewright’s description. "Haven’t you got any clue to their identity, sir?" asked the inspector, who remained at his side. "None; it happened during my absence. They tied up my friend and gagged him. I came across country in my flying machine yonder." "They’ll lose this boat for certain," said the inspector, as the steamer’s warning siren sounded. "You’re sure they are Frenchmen?" "Yes; well, they left a French newspaper behind them." "Do you happen to have it with you?" Burton drew the crushed paper from his pocket, and handed it to the policeman, who unfolded it, and displayed a torn sheet, with only the letters IND remaining of the title. "That’s the _Indépendance Belge_," said the inspector at once. "I expect they’re Belgians, and aren’t coming here at all. Ostend’s their mark, I wouldn’t mind betting." "Via Dover, of course. Is there a boat?" "One at 4.30, sir. I’m afraid they’ve dished you." "I’m not so sure about that," said Burton, glancing at his watch. "It’s now 4.20; this boat’s off. If the Ostend boat is ten minutes late too I can get to Dover in good time to have it searched." "Then if I were you I’d lose no time, sir, and I hope you’ll catch ’em." Burton raced back to the boat that had brought him ashore. In five minutes he was on his own vessel, in two more he was in full flight before the favouring wind, and at 4.35 he dropped on the water in the lee of the Admiralty pier at Dover. But he had already seen that he was too late. The boat, which had evidently started on time, was at least half a mile from the pier. "Yes, sir, I did see a big foreigner go on board at the last minute," said the policeman of whom Burton inquired ten minutes later. "He was carrying a small brown leather hand-bag. I took particular note of him, because he blowed like a grampus, and took off his hat to wipe his head, he was that hot." "Was he bald?" "As bald as the palm of your hand. A friend of yours, sir?" "No," said Burton emphatically. "He’s got away with a secret worth thousands of pounds--millions perhaps, to a foreign navy." The policeman whistled. IV Burton stood looking at the diminishing form of the steamboat. The constable touched his sleeve. "You see that gentleman there, sir?" he said. Following his glance, Burton saw a slim youthful figure, clad in a light tweed suit and a soft hat, leaning over the rail. "Well?" he asked. The constable murmured a name honoured at Scotland Yard. "Put the case to him, sir," he added; "he can see through most brick walls." Burton hastened to the side of the detective. "A man on that boat has stolen the secret of the new explosive for the British Navy," he said without preamble. "Can you stop him?"