He did not complete the sentence. Shouts echoed along the corridor behind them. Dick replaced his hood, handed the keys back to the girl. "Take Mr. Hargreaves to any place of temporary safety you can," he said. "And Mr. Evans. I'll hold them!" "It's right here. This door!" panted the girl, indicating a door at the end of the passage. The three ran toward it. Dick turned. Five or six guards with Von Kettler at their head, were running toward him. They saw the three fugitives and set up a shout. Dick had a quick inspiration. He dashed back into the cell, seized the light bed, and dragged it through the doorway into the passage, just in time to send Von Kettler and two others sprawling. He brought down the bar upon the head of one of them, shouting as he did so. Then he became aware that the passage was flooded with sunshine. Fredegonde had got the door open. He darted back, passed through in the wake of the three, and slammed it shut. Fredegonde turned the key. Instantly Dick found himself with his three companions upon the prairie. Not a vestige of the buildings was apparent anywhere, except for the patches of brown earth. CHAPTER XII _Von Kettler's End_ Fredegonde took command, repressing her agitation with a visible effort. "They cannot break down that door," she said, "and they dare not ask for another key. It will take them a minute or two to go back and reach us around the building. But there may be a score of people watching us. Let us walk quietly toward the thickets. If I am present, they will not suspect anything is wrong." But Dick stood still, driven into absolute immobility by the conflicting claims of duty. For overhead, high in the blue, was an American dirigible. And at his side was the President of the United States. One or other of them he must sacrifice. He chose. He ran forward without answering. Those squares of brown earth, set side by side, were the airplane hangars, and he meant to seize an airplane, if he could find one beneath its coat of invisibility, and fly to warn the dirigible and the fleet. A curious wind was blowing. It seemed to come swirling downward, as no wind that Dick had ever known. It was growing in violence each moment, beating upon his face. As he ran, he was aware of Luke beside him. He heard shouting all about them. Luke had been seen. Not only Luke, but Hargreaves, who was running after Luke, with Fredegonde trying in vain to change his intentions. At the edge of the first brown patch Dick collided violently with the wall of the invisible hangar, and went reeling back. The shouts were growing louder. "Wait!" gasped Luke Evans. He had something like a large watch in his hand. He held it out like a pistol, and from it projected a beam of the black gas. Then Dick remembered Colonel Stopford's words: "He showed me a watch and said the salvation of the world was inside the case. I thought him insane." * * * * *