"What do you think of that?" whispered Bob. "Bluff," said Hugh. "She's clever." The crowd began to break up and presently was moving up and down the street again. Lena started on her way once more, and almost at her heels followed Bob and Hugh. They were beginning to wonder whether they were following a false clue. It might be that Lena had dropped a message on the porch of the house on Elm Street, and if so her work was probably done and there could be no object in following her farther. Suddenly Hugh seized Bob by the arm. "Look at this man coming," he hissed. Not thirty feet distant and walking directly toward them was the false detective. There could be no mistaking him. Bob and Hugh, forgetting for the moment that they were disguised were fearful lest he should recognize them as well. A moment later, however, an interesting event happened right before their eyes, and they forgot all else. As the "detective," the man with whom they had fought that morning, the man who had blown up the deserted house, and whom they suspected of having tried to blow up the railroad bridge in the afternoon, passed Lena he held a slip of paper in his left hand. As she went by she took it with her left hand, though as far as the boys could see the two conspirators had not even looked at each other. Lena continued on down the street as if nothing had happened, while the detective also kept on as though unconscious of having seen Lena at all. He passed the two boys without even a glance. Bob and Hugh stopped short. "What do you think of that?" demanded Hugh. "What'll we do?" "Follow them," said Bob quickly. "You follow him and I'll trail Lena." Without another word the two boys separated. CHAPTER XXII BOB ACTS QUICKLY Bob had almost lost sight of Lena through this temporary delay and he hurried ahead through the crowd, bumping into several people, and drawing black looks from many for his rudeness. He was in a hurry, however. He had to catch up with Lena, and there was no time to be polite. Lena too was hurrying. She threaded her way in and out among the throngs of people, and Bob was hard put to it to keep pace with her. As he rushed along he became more and more puzzled and confused as to what was taking place. There was no doubt in his mind that Lena and Heinrich were working in the interests of Mr. Wernberg and therefore were to be watched closely. Apparently Lena was in league with the fake detective too, else why should he stealthily slip a communication into her hand? But the detective had blown up the house when Mr. Wernberg was within it and had nearly caused his death. If they were all working together how was that fact to be reconciled with what had befallen him? Probably Mr. Wernberg had been injured accidentally as Sergeant Riley had explained. At all events Lena was hurrying along through the crowd and Bob's task was to follow her. His father was watching Heinrich and it would never do for Bob to let his quarry escape him.