For a fraction of a second Joan's slender figure was outlined in the very heart of the ruddy glow, then vanished completely. There was left only a short length of the switch cord to indicate that the girl had ever stood there. Powell reached the mechanism and shut off the projector's flame, then turned swiftly to the control-panel of the recall mechanism. As he closed the switch on this panel, three banks of tubes set in triangular form around the floor-plate upon which Joan had stood glowed a brilliant and blinding green. Shielding his eyes from the glare with an upraised forearm, Powell began stepping a rheostat up to more and more power. In his anxiety, he increased the power far too quickly. There was a sudden gush of blue-white flame from the heart of the mechanism, together with the hissing crackle of fusing metal. The green light in the tubes promptly died. Benjamin Marlowe was bending over the apparatus almost instantly. A moment later he raised a face that had suddenly gone white. There was terror in his eyes as he turned to his assistant. "The entire second series of coils is burned out, Larry!" he gasped in consternation. "Joan is marooned over there in Arret--marooned in that grim unknown land as completely beyond our reach as though she were upon one of the moons of Mars!" For a long moment the two men gazed at each other with horror-stricken faces, dazed and shaken. Then they quickly drew themselves together again and set about the herculean task of making the necessary repairs to the damaged mechanism in time to rescue Joan before the twelve-hour limit should doom the girl to forever remain an exile in that land of alien mystery beyond the atomic barrier. * * * * * Their previous experiments with animals had proved that no living creature from Earth could be brought back after it had been in Arret over twelve hours. After that time the change in the atoms constituting living tissues apparently became permanently Arretian, for the Silver Belts returned without any trace of their original wearers. The necessary repairs to the damaged coils were of such an exacting and intricate nature that any great speed was impossible. Hours passed while the two men bent to their work with grim concentration. Neither of them dared think too much of what nameless dangers might be confronting Joan during those weary hours. Their actual knowledge of Arret was so pitiably slight. Some months ago, while they were experimenting upon apparatus for reversing the electrical charges of an atom's electrons and protons, they had first stumbled upon the incredible fact that such a place as Arret really existed. They found that it was another world occupying the same position in space as Earth, with the fundamental difference in the two interwoven planes of existence lying in the electrical make-up of the atoms that constituted matter in each plane.