"Carton, I'm glad to see you," the scientist greeted him. "You were here with us last night when the Invisible Master came in and went out, and I'd like to hear what you think of a scheme that I've devised for combatting him." "You've found a way to capture him?" Carton burst out. Grantham shook his head. "No, but a way of curbing his activities, I think. Suppose that inside that bank he robbed today there had been a steel barrier, and that entrance to the bank was only through a turnstile like a subway turnstile. Then a guard standing beside it could watch it and if it turned with no one in sight he would know the Invisible Master had entered and could give the alarm. There could be entrance and exit turnstiles like that, and in stores and the like as well as banks. It would stop these snatch-robberies on the part of the Invisible Master, to some extent, at least." "It sounds feasible," Carton admitted. "But it will slow business--do you think the banks will adopt it?" "They will," Wade said shortly. "They're scared stiff down in the financial district over this Vance National robbery today, and they'll catch at any straw to keep the Invisible Master away from their vaults." The Second Blow "Even this, though," Grantham said broodingly, "won't completely stop the Invisible Master. The best it can do is to curb him for a time until we find some way of--" He stopped as the phone-bell rang, and when he had answered, turned the receiver over to Wade. Carton saw the detective's sleepy eyes widen a trifle as he listened to the excited voice on the other end, though his jaws moved his gum as imperturbably as ever. When he turned back to the other two they were waiting in breathless silence. "Headquarters," he said simply. "Less than a half-hour ago the Invisible Master took forty thousand from the pay-office of the Etna Construction Company, up in the Bronx, and shot and killed one of the pay-clerks." "Good God!" Grantham exclaimed. "And they're sure it was he?" "No one else," said Wade laconically. "The office is a small wooden building on the construction lot. The two clerks, Taylor and Barsoff, had the money ready to pay out through a window in one side. There were three guards around the building, armed, and one of them saw the door fly suddenly inward and then heard the shot and scream from inside. They rushed to the office but when they got there Barsoff was dead, shot through the heart, and Taylor could only stammer that the door had flown open, the money had suddenly disappeared, and that Barsoff had been shot out of empty air when he had grasped after it. The guards and Taylor searched the lot and called the police instantly but they've found no trace of him." "Lord!" Carton exclaimed. "The city will go crazy over this--the Invisible Master striking again on the same day!"