Jonner expected the spy to make some move here, tonight, and he had prepared for it on the way from the desert. One earphone of his helmet receiver was tuned with his speaker to the Rebel band they used, the other was tuned to the local frequency used by Marscorp. Jonner listened with one ear to the occasional reports and orders that were passed around the spaceport. Jonner punched Tyruss, next to him, twice on the shoulder. It was the signal. The six men rose and moved forward together. The sentry who loomed before them had no chance. A heat-gun beam is invisible. They cut him down and scurried to the edge of the spaceport, into the circle of light, running in long leaps toward the nearest G-boat. It was as they broke from the canal sage that the thing happened which Jonner had expected. The words were shouted into the earphone attuned to the Marscorp band: "Attention, Marscorp! Att...." Jonner pressed a button on his belt, and his other defense went into action. A scrambler beam cut in on the attempted warning, and everything on that channel dissolved into a buzzing roar. Jonner cast a glance down the line of his companions, but they were too far separated for him to see whether any of them was talking into his helmet microphone. Some of the workmen at the far G-boat saw them running across the field, and scattered in alarm, but the scrambling prevented them from warning others through helmet communicators. The guard at the G-boat that was their goal saw them when they were fifty feet away. He was cut down as he tried to duck around the G-boat. They ran up the ramp. Jonner, first to reach the port, stopped and tried to watch his companions as they hurried past him. Tyruss was fumbling at some control on the belt of his marsuit. His radio channel control? Armed men were converging on the G-boat from all over the field as Jonner slammed and fastened the port. They scrambled up to the nose of the G-boat, and he and Tyruss sank into the pilots' seats. "Strap down for blast-off!" shouted Jonner, and wished viciously that the spy would still be tuned on the Marscorp band and fail to hear him. But everyone strapped down, hurriedly. A score of Marscorp soldiers were standing around the G-boat, firing up at its ports with heat-guns. The beams were futile, for G-boats were built to stand frictional temperatures it would take a heat-gun minutes to build to. Halfway across the field, a squad of men wheeled an anti-tank gun into position. The gentle gravity of Mars quadrupled as the G-boat strained upward on roaring jets, gathering speed. Through the port, Jonner saw the anti-tank gun's muzzle elevate and blossom flame. There was no impact; and there was no opportunity for another shot. The G-boat curved eastward in a long ascending arc. The first stage dropped off over the Aerian Desert, and in a few moments they were in free fall. * * * * *