The second destroyer, in no way daunted by the fate of her colleague, rushed to the attack. Dr. Bird pounded his key frantically in an attempt to turn her back. His message was too late or was misunderstood. Straight over the submarine went the second ship. Again came the red flash. The forward half of the destroyer disappeared and the stern slid down into a huge hole which had opened in the water. "He's invulnerable!" cried the doctor. He pounded his key with feverish rapidity. The two remaining destroyers slackened speed and veered off. Slowly, as though loath to turn their backs on the enemy, they headed out for the broad Atlantic and comparative safety. The submarine went slowly on her way. She did not turn west at the mouth of the Potomac but continued on up the bay. As long as there was light enough, the doctor's plane kept above her but the fading light soon made it impossible to see her. When she had disappeared from view, the doctor reluctantly gave the word to return to Washington. * * * * * "Where do you suppose he will attack next, Doctor?" asked Carnes when they sat again in the doctor's private laboratory. "Washington, of course," said Dr. Bird absently as he looked up from a pile of telegrams he was running through. "Why Washington?" "Use your head. Representatives of every civilized power are in Washington now at the President's invitation to consider means of halting the anti-religious activities of the Soviets. The destruction of the city and the killing of these men would be a telling blow for Russia to strike." "But, Doctor, you don't think--" "Excuse me, Carnes; that will keep. Let me read these telegrams." For half an hour silence reigned in the laboratory. Dr. Bird laid down the last message with a sigh. "Carnes," he said, "I'm check-mated. I sent out a hundred ultra-sensitive short wave receivers yesterday. Four of them were located within fifty miles of Wilmington, North Carolina. One of these four was destroyed, but none of the others detected a sign of a wave during the attack. One of them was within a hundred feet of the edge of the hole. If he isn't using a ray of some sort, what on earth is he using?" "It looked like a flash of red light when it came from the submarine." "Yes, but it couldn't be light. Let me think." The doctor sat for a few minutes with corrugated brows. Suddenly he sprang to his feet. "I deserve to be beaten," he cried. "Why didn't I think of that possibility before?" * * * * * He hurried into his laboratory and brought out a small box with a glass front. From the top projected a spike topped with a ball. Through the glass, Carnes could see a thin sheet of metal hanging pendant from the spike.