"I don't know," Helen answered in a troubled tone. "I'm afraid. Afraid for all humanity. On the television, I've seen enough of Mars to be sure that it is a world of machines, controlled by one Master Intelligence. And even that may be a machine. We make machines that compute the tides and carry out other computations that are almost beyond the power of the human mind: why couldn't a machine think? "The Master Intelligence of Mars plans to add the Earth to his domain. Unless we can do something to stop it, in a few years the world will be overrun with gigantic robot-machines, controlled by force from across the gulf of space. Humanity cannot resist them. Imagine a battleship pitted against that green annihilating ray, and all the other science of an elder planet! "Life is to be blotted out! The Master Intelligence of Mars will rule two worlds of mechanical monsters!" Dan sat in a dazed vision of horror to come, until Helen straightened up as if shaking off a mantle of fear, and smiled heroically, if a bit wanly. "Now you must eat your bread and sardines, to give you strength to fight for humanity!" she cried, with a laugh that she strived, not too successfully, to make cheerful and gay. Obediently, he began to eat, finding an excellent appetite.... It was several minutes later that he fancied he heard a whirring and crackling in the brush behind them. He sprang to his feet in alarm. "It can't be far back to where I left the machine," he cried. "Do you suppose there's danger that--" The mechanical ears of the metal things may have picked up the sound of his voice: but in any event, green flame flashed about them on the instant. Feeling a sudden protective impulse, Dan started toward Helen. That was his last recollection, before what seemed a terrific concussion swept him into the abyss of unconsciousness.... * * * * * His first thought, when he awakened, was of the girl. But he was alone in the silence of the canyon. He sat up, realizing that many hours had passed, for the air was growing cool again, and the sun was low behind the peak at the head of the ravine. The huge, mysterious machine of the purple ring and the vibrating white needle were blazing splendidly. He took more detailed stock of his immediate surroundings. The tangle of brush that had sheltered them had been cut away by the green annihilating ray. Charred stumps remained to show where it had fired bushes beyond the trail. His own shoulder was blistered, a hole was burned in the sheet wound about him, and the hair was singed from the back of his head. Suddenly trembling with horror, he looked about for anything to show that Helen had perished by the ray. Discovering nothing, he breathed a sigh of relief. "She must be still alive, anyhow," he muttered. "And I've had another lucky break! The ray was too high to get me. They must have left me for dead."