"What's the matter, old man?" the first officer asked, smiling straight at him. "Aren't you glad we won through?" "Of course," answered Keith with a tired smile in return. "But why did you look that way?" Graham persisted. And Keith Wells told him: "I was just wondering if Hemmy told the truth." The Black Lamp _By Captain S. P. Meek_ [Illustration: _"Look out!" He leaped to one side as he spoke._] [Sidenote: Dr. Bird and his friend Carnes unravel another criminal web of scientific mystery.] "The clue, Carnes," said Dr. Bird slowly, "lies in those windows." Operative Carnes of the United States Secret Service shook his head before he glanced at the windows of the famous scientist's private laboratory on the top floor of the Bureau of Standards. "I usually defer to your knowledge, Doctor," he said, "but this time I think you are off on the wrong foot. If the thieves came in through the windows, what was their object in cutting that hole through the roof? The marks are very plain and they indicate that the hole was cut in some manner from the inside." Dr. Bird smiled enigmatically. "That is too evident for discussion," he replied. "I grant you that the thieves entered from the roof through that hole. After they had secured their booty they left by the same route. I presume that you have noticed the marks on the roof where an aircraft of some sort, probably a helicopter, landed and took off. A question of much greater moment is that of what they did before they landed and cut the hole." "I don't follow your reasoning, Doctor." "Carnes, that hole was cut through the roof with a heavy saw. In cutting it, the workers dislodged quite a little plaster which fell to the floor and must have made a great deal of noise. Why wasn't that noise heard?" "It was heard. The watchman heard it, but knew that Lieutenant Breslau was working here and he thought that he made the noise." "Surely, but why didn't Breslau hear it?" "How do we know that he didn't? He was taken to Walter Reed Hospital this morning with his mind an absolute blank and with his tongue paralyzed. He must have seen the thieves and they treated him in some way to ensure his silence. When he is able to talk, if he ever is, he'll probably give us a good description of them." * * * * * Dr. Bird shook his head. "Too thin, Carney, old dear," he said. "Breslau is a very intelligent young man. He was perfectly normal when I left him shortly after midnight last night. He was working alone in here on a device of the utmost military importance. On the desk is a push button which sets ringing a dozen gongs in the building. Surely a man of that type would have had sense enough when he heard and saw intruders cutting a hole through the roof to sound an alarm which would have brought every watchman on the grounds to his assistance. He must have been knocked out before the hole was started, probably before the helicopter's landing."