e're not the hunters, Dick Rennell," went on Colonel Stopford. "We're hiding under cover, and I'm counting on you to turn the tables. They even know my office is here. I had a long distance call from Savannah this morning in mocking vein. They advised me to have the White House watched to-night. I warned the President, and we've posted guards all round it."
"They held the wire while you called up the President?" asked Dick.
"Damn it, no! They called me up from Scranton the instant he'd finished speaking. They have the power of the devil, Rennell, with that infernal invisibility invention of theirs. Rennell, we're fighting unknown forces. Who this Invisible Emperor is, we don't even know. But one thing we've found out. He has his headquarters somewhere in your district. Somewhere along the south Atlantic seaboard. The greater part of his activities emanate from there. But we're fighting in the dark. The clue, the master clue that will enable us to locate him—that's what we lack."
The sun had set, it was beginning to grow dark. Colonel Stopford switched on the electric lamp beside his desk.
"What have you to say, Rennell?" he asked; and Dick was aware that the two other men were regarding him attentively.
"It's evident," said Dick, "that Von Kettler possessed this means of invisibility in his cell, and wasn't detected. He simply slipped out when the guard came to fetch him."
"Invisibility? Yes! But invisible's not the same thing as transparent," cried Stopford. "These folks have operated in broad daylight. They're transparent, damn them! Not even a shadow! You know what I mean, Rennell! What I'm thinking of! That crazy man you were in touch with six months ago, who prophesied this! We turned him down! He showed me a watch and said the salvation of the world was inside the case! I thought him insane!"
