"Lesson number one about being too sure," grumbled disappointed young Benson. "However, we'll soon come upon another policeman." Two blocks more were covered, however, without sighting a bluecoat. Jack even began to wonder how it would do to leap upon Millard, calling upon passing citizens to aid him until a policeman arrived. "But that would be a two-edged sword, that might cut too keenly on the wrong side," reflected the submarine boy. "Millard would be sure to claim that I was assaulting him. It would look like that, too, and I'd probably get a thumping from the crowd, while Millard slipped away. Then he would be warned that he was wanted, and he'd make himself mighty scarce after that." Still no policeman came into sight. "Gracious!" muttered Jack Benson, suddenly. He had just glanced into a store's show window, where a mirror was set at an angle. The submarine boy, looking into that mirror, became aware that he could see people at a considerable distance behind him down the street. "I wonder if Millard has been taking sights, too, and has had a peep at me, that way?" muttered the boy. At the next corner the long-legged one, after a brief look down the side street, turned into it. "Now, that we're getting away from the main street there'll be far less chance of finding a police officer," sighed Jack, at last wholly discontented with luck. Millard led without, apparently, ever thinking to glance back. He turned a second corner, into another small street, and kept on. "This is getting more exciting," muttered the young trailer. "Yet all signs point to the fact that I've got to make the grab all by myself. I wonder if I can down that chap and get the upper hand of him? I don't mind a thumping, but I'd be sadly ashamed of myself to let the fellow get away from me." Millard was walking briskly, now. Next, he turned sharply to the left. "Ah!" Then Jack Benson shot swiftly forward on tip-toe, trying to make no noise as he ran. For the long-legged one had, to all seeming, at the distance, wheeled and gone through the wall of a brick building. Just an instant later, however, this impossible feat was explained. The submarine boy found himself at the street-end of a narrow alley between two brick buildings. "He has gone into the rear house, at the end of the alleyway," decided Benson, peering down this narrow thoroughfare. "He has left the door partly open, too. I'll have to have a look-in." As he stole down the alley-way Jack Benson was too sensible, and by this time, too much experienced in the ways of a rougher world, not to suspect that there might be some trap in that door partly open. "He may have seen me, and may have left that door open on purpose," Benson reflected. "He may be lying in wait for me, inside. Or else he may have left that door open, just to make me suspect a trap and keep out. In the meantime, he may be slipping through a door on the other side of the house, and sneaking away from me."