They knew Roque! Heinrich Hume, aviation lieutenant, who usually had a good deal to say on those grounds, made no more protest than a clam at this interruption of a special aëroplane test. He simply waved two other aviators on duty into the machine, as Billy and Henri marched meekly away with the imitation merchant. While many of the spectators marveled at the apparent breach of discipline, the lieutenant was content to let them wonder. At least, he offered no explanation. Billy and Henri did a lot of thinking as they crossed the parade ground--there must be something brewing, or Roque would not have been so impatient as to invade the parade ground at the time he did. Roque conducted the boys into Lieutenant Hume's private office at headquarters, closed and locked the door behind them. Removing his spectacles, and throwing his slouch hat among the maps that littered a big table in the center of the room, the secret agent at the same time changed his form of address--the oily manner was succeeded by abrupt and stern speech, which showed the real man of brain and unlimited authority. The secret agent had seated himself, without invitation to the boys to do likewise. They stood, facing the real Roque they knew by former experience. "Where is Ardelle?" Roque put the question like a pistol shot, and fiercely eyed the youngsters before him. The point-blank query failed to reach the mark intended. Billy looked at Henri and Henri looked at Billy, and then they both looked at Roque with never even a quiver of an eyelash. They had not comprehended what was behind the dreaded agent's snapshot at their nerves. The truth of the matter was, they did not know anybody by the name of "Ardelle." So Billy, with a bold front, remarked: "You can't prove it by us, sir. Mr. Ardelle is not in our list of friends." "None of that!" Roque pointed a menacing finger at the astonished pair of youngsters. "I have it beyond doubt that Ardelle was on these very grounds a day or two ago, and by the word of a man who could not be mistaken. Fool that he was not to be sure at the time, and only the garb of a sailor to mislead him." Then it jointly dawned upon the minds of Billy and Henri that Anglin, the smiling secretary of the eminent director of affairs at Calais, and later in the rôle of a bubbling sailor here in faraway Hamburg, must be the Ardelle about whom Roque was talking. They realized, too, that through their boyish delight in lending aid and a helping hand to one they had known in intimate association with that best of friends in France, they had unconsciously maneuvered themselves into a dangerous game, a slip in which meant a dance with death. A tissue message from this very suspect that Roque was so eager to apprehend even then burned against the breast of Henri, a little wad of paper that now represented the price of the world to a pair of bright boys.