The entire rescue crew were coughing violently as the ambulances left Michaelville. For a mile they drove through fog that was thicker than had been seen in Maryland for years. They reached the point where they had encountered the congealed moisture on the way out, but now there was no diminution of its density. The main post was less than two miles away when they burst out into a clear night and increased their speed. As the two machines drew up in front of the post hospital, the driver of the leading ambulance swayed in his seat. Blindly he pulled on his emergency brake and then slumped forward in his seat, his breath coming in wheezing gasps. Major Martin hastily tore the mask from his face and glanced at it. "Take him in with the rest!" he cried. "His mask must have leaked." As they entered the hospital, a sickening weakness overcame Major Martin. From all sides a black pall seemed to roll in on him and bits of ice seemed to form in his brain. He reeled and caught at the shoulder of a corps man who was passing. The orderly caught at him and looked for a moment at his livid face. "Sergeant Connors!" he cried. A technical sergeant hastened up. Major Martin forced words with difficulty through stiffening lips. "Call Captain Murdock," he wheezed, "and have him get Captain Williams. I'm down and probably Dr. Briscoe will be down in a few minutes. Telephone the commanding officer and tell him to quarantine the whole proving ground. Have the telephone orderly wake everyone on the post and order them to close all windows in all buildings and not to venture outside until they get fresh orders. This seems to be the same stuff they had in Belgium last December." As the last words came from his lips he slowly stiffened and slumped toward the ground. The sergeant and the orderly picked him up and carried him to a bed in the emergency ward. The orderly hurried away to close all of the hospital windows while Sergeant Connors took down the receiver of the telephone and began to carry out the Major's orders. * * * * * Dr. Bird glanced at the news-paper clipping which Operative Carnes of the United States Secret Service laid on his desk. Into his eyes came a curious glitter, sure evidence that the famous scientist's interest was aroused. "Last December when we discussed this matter, Doctor," said the detective, "you gave it as your opinion that Ivan Saranoff was at the bottom of it and that the same plague which devastated the Meuse Valley in Belgium would eventually make an appearance in the United States. You were right." Dr. Bird bounded to his feet. "Is Saranoff back on this side of the Atlantic?" he demanded. "Officially, he is not. Every customs inspector and immigration officer has his photograph and no report of his arrest has come in, but we know Saranoff well enough to discount negative evidence where he is concerned. Whether he is here or not, the plague is." "When did it appear?"