Not that of invisibility. Dick stared about him in bewilderment. For a moment, before he quite realized what had happened to him, he thought he had lost his mind. Underneath him was a thick rug, beneath his head a pillow; he could feel both of them, and yet all he could see was the open country, a clearing with shrubbery on either side, and, beyond that, a luxurious growth of tropical trees. Under him, to all visual appearance, was the bare ground. He moved, and heard the clank of chains. He looked down at himself. His wrists were loosely linked to a chain that seemed to stretch tight into vacancy and end in nothing. His ankles were bound likewise. And both chains appeared to be of solid silver, but thick enough to give them the strength of iron! Then he perceived that old Evans was bound in the same way. "Rennell! Rennell!" repeated the old man in a sort of whimper. "Thank God you've come out of it! I was afraid you were dead." "What's happened?" asked Dick. "Where are we? Didn't they get us?" "They've got us, damn them!" snarled old Evans. "All the rest burned to cinders, those fine fellows, Rennell! You were thrown unconscious, but none of my tough old bones were hurt. They pulled us out of the wreckage and brought us in here and tied us with these silver chains." "In here? But where are we?" demanded Dick, trying to pass his hand across his aching forehead, and realizing that the chain, though it seemed fastened to nothing, was perfectly taut. * * * * * "In one of their damned invisible houses," whimpered the old man. "They're fireproof. Nearly all our bombs fell on the tarmac, and they did hardly any damage at all. One of those devils was bragging about it to me. I couldn't see anything but his eyes. And they've taken away my gas-box," wailed old Luke. Dick cursed comprehensively and was silent. The burning rage that filled him left him incapable of other utterance. Silver chains! They must be madmen--yes, that was the only explanation. Madmen who had escaped from somewhere, obtained possession of scientific secrets, and banded themselves together to overcome the world. If he could get the chance of a blow at them before he died! He heard a door swing open--a door somewhere out on the prairie. Two men sprang into sudden visibility and approached him. There was nothing invisible about these men, though they had seemed to have materialized out of nothing. They wore the same black, trimly fitting uniform that Dick had seen in the White House. They were flesh and blood human beings like themselves.