Clee ran to where he had left the invisible man, cursing himself under his breath for being an utter ass for not having guessed this. His groping fingers quickly found the squirming Xantra's neck; and he had begun to throttle him into unconsciousness when Vivian called out: "No! Don't! That won't stop the slaves: they've already been given the order! We've got to make Xantra stop them! Here--drag him to the work-table! I've got something--" Wondering what the girl was about, Clee relaxed his grip on the invisible man's neck and complied. But he suddenly understood--and Jim, too--when he saw coming through the air the pair of thought-sending helmets. He had a way of communicating with Xantra, of course! He saw the larger helmet lower to rest over the head he was still holding; then soft hands placed the other over his own. As it settled down a great crash sounded in the other room: the door had given in. It was still held almost in place by the tightly-wedged furniture, but that would not hold the animal-men long. "Hurry!" cried Jim. "I'll stand by the door!" And he was already on his way to it. Clee saw the small panel on the table above; saw the knob on it turn. He caught Vivian's excited voice. "Tell him to order them to stop," she said; "or else--or else--" "He dies!" finished Clee, viciously thumbing into the air where the invisible Xantra's neck was. * * * * * With all the intensity he could muster, Clee concentrated on one simple, strong thought. He hardly heard the triumphant cries of the slaves as they felt the blocking furniture give before their efforts; all his energy was being expended in the will to get his thought across. "Tell those slaves to stop breaking in or you die!" he commanded. The noises at the door continued. Either Xantra had not understood, or else he was stubborn. He repeated his command and threat, and still the crashing sounds came to his ears. Desperate, he played his last card; and unconsciously his lips formed the words of his next mental command, so that it was understood by the breathlessly watching Vivian. "_Tell them to stop!_" he willed. "_No more air till you do!_" And with the words his fingers closed tightly over the other's throat. The sounds at the door continued; for a moment the invisible form between Clee's knees writhed violently--and then suddenly, almost magically, a silence fell over the whole room. Clee had forced his will on Xantra! He had made him stop the slaves! And just in time. Clee's fingers relaxed a little on the throat of the man beneath him. He turned and said: "Quick, Vivian--find that anaesthetic!" A moment later it was pressed in his hands. "Say when," he told the girl, and held it beneath the nose of the helpless man. Xantra's head at once fell back, and he heard Vivian telling him to stop. He pulled away the bottle, corked it and stood up. "Well, that's that," he said. * * * * *