"In the face of that letter, Dr. Bird," said the major, "I have no alternative to allowing you to enter the cave, but I will warn you that it is at your own peril. I'll give you an escort, if you wish." "If Lieutenant Pearce will come with me as a guide, that will be all that I need." The lieutenant paled slightly, but threw back his shoulders. "Do you wish to start at once, sir?" he asked. "In a few moments. What is the floor of the cave like where we are going?" "Quite wet and slimy, sir." "Very slippery?" "Yes, sir." "In that case before we go in we want to put on baseball shoes with cleats on them, so that we can run if we have to. Can you get us anything like that?" "In a few moments, sir." "Good! As soon as we can get them we'll start. In the meantime, may I look at that gun that was found?" * * * * * The Browning machine-gun was laid before the doctor. He looked it over critically and sniffed delicately at it. He took from his pocket a phial of liquid, moistened a portion of the water-jacket of the weapon, and then rubbed the moistened part briskly with his hand. He sniffed again. He looked disappointed, and again examined the gun closely. "Carnes," he said at length, "do you see anything on this gun that looks like tooth marks?" "Nothing, Doctor." "Neither do I. There are some marks here which might quite conceivably be finger-prints of a forty-foot giant, and those two parallel grooves look like the result of severe squeezing, but there are no tooth marks. Strange. There is no persistent odor on the gun, which is also strange. Well, there's no use in theorizing: we are confronted by a condition and not a theory, as someone once said. Let's put on those baseball shoes and see what we can find out." Dr. Bird led the way into the cave, Carnes and the lieutenant following closely with electric torches. In each hand Dr. Bird carried a phosphorus hand-grenade. No other weapons were visible, although the doctor knew that Carnes carried a caliber .45 automatic pistol strapped under his left armpit. As they passed into the cave the lieutenant stepped forward to lead the way. "I'm going first," said the doctor. "Follow me and indicate the turns by pressure on my shoulder. Don't speak after we have started, and be ready for instant flight. Let's go." Forward into the interior of the cave they made their way. The iron cleats of the baseball shoes rang on the floor and the noise echoed back and forth between the walls, dying out in little eerie whispers of sound that made Carnes' hair rise. Ever forward they pressed, the lieutenant guiding the doctor by silent pressure on his shoulder and Carnes following closely. For half a mile they went on until a restrainable pressure brought the doctor to a halt. The lieutenant pointed silently toward a crack in the wall before them. Carnes started forward to examine it, but a warning gesture from the doctor stopped him.