"Maybe it's one man, maybe there're half a dozen," the chief admitted, "but we've got to nail 'em. The very fact that they haven't started anything of consequence since the early part of the year would appear to point to renewed activity very shortly. It's up to you and the other men already in New York to prevent the success of any of these plots." Walters listened patiently to all the dope that had been gathered and then figured, as had every new man, that it was up to him to do a little sleuthing of his own. The headquarters of the German agents was supposed to be somewhere in Greenwich Village, on one of those half-grown alleys that always threatens to meet itself coming back. But more than a score of government operatives had combed that part of the town without securing a trace of anything tangible. On the average of once a night the phone at headquarters would ring and some one at the other end would send in a hurry call for help up in the Bronx or in Harlem or some other distant part of the city where he thought he had turned up a clue. The men on duty would leap into the machine that always waited at the curb and fracture every speed law ever made--only to find, when they arrived, that it was a false alarm. Finally, after several weeks of that sort of thing, conditions commenced to get on Dick's nerves. "I'm going to tackle this thing on my own," he announced. "Luck is going to play as much of a part in landing von Ewald as anything else--and luck never hunted with more than one man. Good-by! See you fellows later." But it was a good many weeks--August, to be precise--before the men in the Federal Building had the opportunity of talking to Walters. He would report over the phone, of course, and drop down there every few days--but he'd only stay long enough to find out if there was any real news or any orders from Washington. Then he'd disappear uptown. "Dick's sure got a grouch these days," was the comment that went around after Walters had paid one of his flying visits. "Yeh," grunted Barry, who was on duty that night, "either the von Ewald case's got on his nerves or he's found a girl that can't see him." Neither supposition missed the mark very far. Walters was getting sick and tired of the apparently fruitless chase after an elusive German. He had never been known to flinch in the face of danger--often went out of his way to find it, in fact--but this constant search for a man whom nobody knew, a man of whom there wasn't the slightest description, was nerve-racking, to say the least. Then, too, he had met Mary McNilless.