The face of Clee's wrist watch was glowing brightly; it took only a second to find with the package of tobacco a spot which cut the dial's unnatural glow. As they found it the skin on the two men's bodies prickled all over. The line from the dial to the package of tobacco, if continued, would reach a spot on the floor not six feet away. And looking carefully there they could barely make out, in the bent hairs of the rug, a broken outline that might have been made by a prone figure. As they prepared to jump they heard from that place a low sigh--and just before them appeared the distinct print of a human hand. Xantra was rising! And coincident with this a sudden banging at the door told them that the slaves at last had started to break in! As one man the two Earthlings leaped on Xantra; he would have to be taken care of first. When they had fastened on his rising body they punched and pounded it furiously. Though their enemy was undoubtedly only half conscious, the sudden attack aroused him and he resisted vigorously. But then Clee made a lucky connection on what he felt to be his jaw, and the invisible form in their arms went limp. "Get a rope--wire--anything to bind him with--quick!" yelled Clee. "I'll hold him!" The pounding at the door was increasing ominously is Jim dashed over to the work-table. Rapidly he looked for something suitable, and in a few seconds was back with a length of stout wire which they quickly wrapped around the ankles and wrists of the limp form Clee was holding. As the wire touched Xantra it gradually disappeared from their sight, but their fingers reassured them that he was tightly bound. Then they were at the door, which, shivering and bending from the battering without, showed signs of giving in. With herculean efforts they dragged a heavy divan over and wedged it tightly against it; then added other furniture in a tight supporting pile. But the door, of some light metal, was not built to stand such a siege, and was buckling further inward with each blow being dealt it. More and more plainly the two men could hear the triumphant snarls and howls of the animal-men. Frantically they ransacked the rooms looking for what they thought might be weapons, but found none. They looked at each other with dismay. It was only a question of time--minutes--before the slaves would break in. What could they do? * * * * * In that tense moment of indecision a low, weak voice reached their ears--a woman's voice, and one they remembered well. "Vivian!" cried Clee, and ran to the alcove, from whence it had seemed to come. The girl's next words brought them understanding. "Clee--Jim--it's Xantra! He's willing the slaves to break in! He's lying bound on the floor, but he's conscious!"