He swung his pack from his shoulders to the ground, and extracted an obviously self-constructed device which he set on the ground. It had a whip aerial, which he extended. Then he plugged in a considerable length of flexible wire and unfolded a tiny, improvised directional aerial with an even tinier booster at its base. Bordman slipped his pack from his shoulders and watched. Huyghens put a pair of head-phones over his ears. He looked up and said sharply: "Watch the bears, Bordman. The wind's blowing up the way we came. Anything that trails us will send its scent on before. The bears will tell us." He busied himself with the instruments he'd brought. He heard the hissing, frying, background-noise which could be anything at all except a human signal. He reached out and swung the small aerial around. Rasping, buzzing tones came in, faintly and then loudly. This receiver, though, had been made for this particular wave-band. It was much more efficient than the modified space-phone had been. It picked up three short buzzes, three long ones, and three short ones again. Three dots, three dashes, and three dots. Over and over again. SOS. SOS. SOS. Huyghens took a reading and moved the directional aerial a carefully measured distance. He took another reading, shifted it yet again and again, carefully marking and measuring each spot and taking notes of the instrument readings. When he finished, he had checked the direction of the signal not only by loudness but by phase, and had as accurate a fix as could possibly be made with portable apparatus. Sourdough growled softly. Sitka Pete whiffed the air and arose from his sitting position. Faro Nell whacked Nugget, sending him whimpering to the farthest corner of the flat place. She stood bristling, facing down-hill the way they'd come. "Damn!" said Huyghens. He got up and waved his arm at Semper, who had turned his head at the stirrings. Semper squawked and dived off the spur, and was immediately fighting the down-draught beyond it. As Huyghens readied his weapon, the eagle came back overhead. He went magnificently past, a hundred feet high, careening and flapping in the tricky currents. He screamed, abruptly, and screamed again. Huyghens swung a tiny vision-plate from its strap to where he could look into it. He saw, of course, what the tiny camera on Semper's chest could see--reeling, swaying terrain as Semper saw it, though of course without his breadth of field. There were moving objects to be seen through the shifting trees. Their coloring was unmistakable. "Sphexes," said Huyghens dourly. "Eight of them. Don't look for them to follow our track, Bordman. They run parallel to a trail on either side. That way they attack in breadth and all at once when they catch up. And listen! The bears can handle anything they tangle with--it's our job to pick off the loose ones. And aim for the body! The bullets explode."