One of the attackers, more daring than the rest, leaped forward to engage the engineer. He collapsed with a crushed skull. Then, when victory seemed in their grasp, luck turned. At Jack's next blow the stock of his weapon parted from the barrel, leaving him almost defenseless. At the same time Manthis slipped and collapsed from a knife thrust. * * * * * Jack was left alone to face three enemies and would have been killed within the minute had not Solinski, recalling the little time he had left to stop the interfering wave, deserted his comrades and sprinted for the laboratory. The seeming defection of their chief threw the other two attackers into momentary confusion. Before they could recover, Jack knocked one out with the gun barrel, then came a flying tackle at the other. But he had caught a tartar. His remaining enemy was a gigantic Negro. Recovering from his surprise the latter lifted high a glittering knife to finish his disarmed foe. Jack snatched at the uplifted arm--missed! A revolver cracked. The hooded Negro staggered, then crashed forward. "Remembered my pistol just in time," gasped the doctor from the floor. "Don't bother about me. I'm all right. Stop Solinski, for God's sake." Although his lungs seemed bursting Baron turned and flew up the stairs. Being familiar with every turn, he gained on the Russian and caught sight of the dreadful black coat-tails as his enemy burst through to the twentieth floor. The locked door of the apartment baffled him only a moment. Stepping back, Solinski hurled his giant frame against the panels. They splintered and crashed inward. But the delay allowed Jack to catch up. He leaped on the Russian's back. Locked together they reeled into the living room. For a fleeting moment Jack saw June sitting rigidly at the instruments. Her eyes were starting from their sockets but her hands were steady. "I warned you to kill yourself," Solinski's voice rose in a screaming whisper through the respirator. "Now I will do it." Displaying the strength of madness he hurled Jack from him. Losing all control of his limbs, the younger man flew across the room and demolished the divan in his fall. But the thought of what Solinski would do to June brought him back to the attack. * * * * * The fury of their struggle wrecked the living room. Both bled from numerous wounds. One of the Russian's bleak eyes closed under a well-directed blow, but otherwise he seemed unaffected. Jack grappled again and realized his mistake as he was caught in a bone-cracking grip and forced into the laboratory. Baron felt a rib snap. A sweat of agony broke out over his body. Holding his enemy helpless the invader worked his way toward the work table. They bumped against it, making the equipment totter perilously. Solinski released his grip, snatched a bottle of distilled water and swung.