"Don't leave me stuck out here in case they cross at Shepherdsville and come up behind us. I don't want to be cut off." "Don't worry," said Matt. "I'm sending a scout car up the highway toward Elizabethtown. They'll warn us in plenty of time if they come that way." He snapped the radio off and turned to Isaac. "Well, we may as well wait here until Lynn fetches our captives," and lit a cigarette. * * * * * By dark they had all the vital stores and their personal goods transferred from the _Argus_ to the fort. The nineteen women from Margot Drake's band were locked in the jail. The second assistant engineer had dismantled key parts of the rocket ship so that it couldn't be moved. And what was left of the bodies of the former personnel of the fort were being removed from the top floors by a special detail of space-suited men and dumped into the river. Matt himself had seen to it that their defenses were in order. Floodlights illuminated the grounds. The machine guns were oiled and ammunition belts stacked handily. At seven o'clock, he called in Jesse Sawyer. "Take up the machine gun," he ordered, "and let the bridge go. It isn't practical to hold it any longer. I'm calling in the scout car from Elizabethtown." "Good," came Sawyer's relieved voice. Matt detected a note of excitement in it. "Good. I've something important that I want you to see, Matt. Is the microscope set up?" "Not ours," said Matt, "but the fort has some of the finest-equipped laboratories I've ever seen. You can use the one here. What have you found?" "I'll be there in a jiffy. Show you then. But it's big, Matt. It's big. I'll want you and Isaac in the laboratory. Yes, and Frazer, too." The radio clicked off. A frown furrowed Matt's brow. What the hell had Sawyer stumbled across? He had never heard the biologist so urgent before. And Sawyer wasn't an excitable person. He wondered why he wanted Frazer, Isaac and himself all in the laboratory? Suddenly it struck him. Frazer was the biochemist. Isaac, besides being the director, was the expedition's zoologist, and he himself was the botanist! It was not long before the three men were in the organic laboratory. Jesse Sawyer entered, wheezing and dabbing at his moon face with a handkerchief. Matt noticed that he was carrying a specimen jar in his other hand. "What have you found, Jesse?" Matt began, but the fat man waved him to silence. "Not so fast. I want a look at this under the microscope first. Then I want all of you to see it, before I say anything. Where is the microscope? Oh, here." With trembling hands he began to prepare a slide. Matt watched him fascinated, noting the deftness of the biologist's pudgy fingers. At length, perspiring freely, Sawyer put his eye to the microscope, making several adjustments. He drew in his breath sharply.