The duty-man at the exit locks of the main building stood at his window and watched me curiously. He saw me go up the spider-stairs. He could see the figure he thought was Wilks, standing at the top. He saw me join Wilks, saw us locked together in combat. For an instant the duty-man stood amazed. There were two fantastic, misshapen figures swaying in the Earthlight five hundred feet above the camp, fighting desperately at the very brink. They were small, dwarfed by distance, alternately dim and bright as they swayed in and out of the shadows. Soon the duty-man could not tell one from the other. Haljan and Wilks--fighting to the death! The duty-man recovered himself and sprang into action. An interior siren-call was on the instrument panel near him. He rang it, alarming the camp. The men came rushing to him, Grantline among them. "What's this? Good God, Franck!" They saw the silent, deadly combat up there on the cliff. The two figures had fallen together from the observatory platform, dropped twenty feet to a lower landing on the stairs. They lay as though stunned for a moment, then fought on. Grantline stood stricken with amazement. "That's Wilks!" "And Haljan," the duty-man gasped. "Went out--something wrong with Wilks--acting strangely--" The interior of the camp was in a turmoil. The men awakened from sleep, ran out into the corridors, shouted questions. "An attack?" "Is it an attack?" "The brigands?" * * * * * But it was Wilks and Haljan in a fight out there on the cliff. The men crowded at the bulls'-eye windows. And over all the confusion the alarm siren, with no one thinking to shut it off, was screaming with its electrical voice. Grantline, stricken for that moment of inactivity, stood gazing. One of the figures broke away from the other, bounded up to the summit from the stair-platform to which they had fallen. The other followed. They locked together, swaying at the brink. For an instant it seemed to Grantline that they would go over; then they surged back, momentarily out of sight. Grantline found his wits. "Stop them! I'll go out to stop them! What fools!" He was hastily donning one of the Erentz suits which stood at the lock entrance. "Shut off that siren, Franck!" Within a minute Grantline was ready. The duty-man called from the window: "Still at it! By the infernal, such fools! They'll kill themselves!" The figures had swayed back into view, then out of sight again. "Franck, let me out." Grantline was ready. He stood, helmet in hand. "I'll go with you, Commander." But the volunteer was not equipped. Grantline would not wait. "I'm going at once. Hurry, Franck." The duty-man turned to his panel. The volunteer shoved a weapon at Grantline. "Here, take this." Grantline jammed on his helmet. * * * * *