the six men crouched in the concealing canal sage near the edge of marsport, the spaceport outside mars city. the blue mist was a heavy fog that swirled around them.

in the lighted circle of the spaceport area three stubby, two-stage gravity-boats sat upright, about a hundred yards apart. these were the heavy duty rockets that plied back and forth to phobos, mars' inner moon and marscorp's natural space station, entering the planetary atmosphere of mars where spaceships could not go. workmen stirred busily around one of the g-boats; a guard stood at the entrance port of each of the other two.

jonner tried to assess the evidence, to decide which of his five companions was the marscorp spy. how marscorp had found out about the expedition, how the credentials had been forged, how the rendezvous had been learned, did not matter now. marscorp could not know their plans beyond the rendezvous in the desert, because only he and sir stanrich had known the orders sir stanrich had given him for this mission.

the fact that stein and wessfeld had arrived together from charax eliminated them as suspects, for the charax command would have known whether one or two men were to be sent from there.

jonner did not believe tyruss was the spy. jonner had won his space papers just before the rebellion began, but it was logical that sir stanrich would send a more experienced space captain to handle their ship.

that left farlan and aron, from different sections of the hadriacum front. which one? in their specialties, farlan was an alternate to stein as an astrogator, aron an alternate to wessfeld as an engineer. but every spaceman could handle every other spaceman's duties in an emergency, and it was hard to say which task they had decided to double up on.

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.