Doc motioned to his colleagues to retreat with him. They duckwalked back to the end of the block and waited. Barney whispered, 'What's going on, Doc?'

'Keep your rifles ready. We can shoot if we're attacked in here. As to the strange behaviour of the animals and birds, I'll explain when I'm certain of its cause.'

The screams went on for about ten minutes and then died out. The only sound was Pauncho's heavy breathing and the ripping of flesh as the birds tore at the corpses. Doc, not wanting to make any noise at all, put his hand on each man's arms and transmitted in Morse with the pressure of his fingers.

'The hemispheres may be electronic devices to control the animals by remote control. It's possible that the operator thinks his enemies are all dead and has shut down control. In which case, we might be able to stroll on by the birds without their attacking us. I say we should try it.'

Barney and Pauncho simultaneously squeezed back, 'You're the boss, Doc. You give the word.'

He transmitted, 'Ordinarily I would. But this is a very bad situation, and I would not blame you one bit if you decided to retreat now so we could fight later - in a situation more advantageous to us.'

'If we go back, will you go back with us?' Barney transmitted.

Doc hesitated and then said, 'No.'

'Then we'll go on with you. Don't you like us, Doc, you want us to miss out on this? We have to earn our immortality.'

Doc smiled slightly, and it was a measure of how deeply he was affected that he allowed his self-control to lapse even this much. Or perhaps it was a measure of his progress in getting rid of the too-rigid self-control of his past. He was trying to act more humanly, or more openly, since being too self-controlled was as human as not being self-controlled enough.

'O.K.,' he squeezed back. 'You cover me from the entrance. If they attack, I'll drop on my back and shoot upward, and you fire over my head.'

He waddled into the room, straightened up, and walked toward the nearest body and the golden eagle feeding on it. The eagle looked fiercely at him and turned on top of the corpse, flapping its wings. Its beak opened as if it were uttering a silent cry. But it did not fly away. Nor did it attack. And the other birds continued to eat after glaring at him and assuring them-selves that he was not belligerent.

Doc turned to signal to the two. Barney shouted, 'Lookout, Doc!'

He wheeled, bringing up his rifle, having heard the flap of wings at the same time that Barney yelled. The vulture flew at him with beak and claws outspread, and behind him was the thunder of two dozen pairs of wings. All headed toward him.

He fell on his back, firing as he did. The vulture flew bloodily apart and spun to one side under the impact of the bullets. Blood and feathers and flesh spattered Doc. He continued to fire at the great birds, and then the explosions of his colleagues' FN's were added to his. Bullets ricocheted off the walls and the ceiling, wheeing by him, and his face stung from chips of stone. But the birds blew apart from the many high-velocity bullets striking them. And when Doc and the two men had emptied their magazines, they dropped the rifles and began firing with the 15-calibre explosive bullets from their gas guns. Able to see in the blacklight, they had no trouble aiming, and within sixty seconds all twenty-four birds were heaps of feathers.

Doc jumped up and ran toward the entrance of the tunnel as they quit firing and dived into its shelter.

Pauncho said, 'What's up, Doc?' but Caliban did not reply.

He waited for some sign of action, knowing that the renewal of attack by the birds probably meant that the operator had happened to look into the room and see him. Or perhaps it meant that the operator had seen him from the first but had not stimulated the birds until he thought Doc was off his guard. It also meant that the operator could have a form of blacklight, since Doc had stayed out of range of the beams of the flashlight still operating.

Nowhere was there any evidence of TV cameras or one-way windows, but it would be easy to simulate rock.

There was a groaning behind them and a trembling of the floor. They turned to see the huge stone block withdrawing into the wall. The heads of the collapsing bodies struck the stone with a plop.

Doc nodded, and they got up and walked across the room, pausing only by the bodies to shove an extra magazine into their capacious jacket pockets. The exit was another archway at the far wall. They looked down its round length. Doc wondered why the tunnel was round instead of square, as all the others had been. It went for at least forty yards before making a turn. The roundness might preclude any section of the wall sliding out to crush them. At least, the interior was smooth, seemingly carved out of the granite. But material in paste form, looking like stone, could have been spread over to cover up the lines of demarcation of a separate piece. He whispered to them, and they walked to the tunnel and entered, crouching. They held their rifles across their bellies so that the muzzle and stock extended past their sides.

They had gone ten yards when the wall to their right crumbled and flew outward, propelled by a block of stone. The mass squealed as it slid across the floor - but not loudly, indicating that the bottom was lubricated - and then the three were knocked side-wise. But the block stopped short with a crash; their rifles acted as rigid bars to hold the block back. And it was evident that there would be no more pressure put on them. The rifles had bent just a trifle but showed no signs of increasing buckling.

Doc crawled over his rifle and scooted on out past the block. He felt naked without the rifle to keep off the block, even though he knew that the three already wedged in were doing their work. Pauncho and Barney came after him with Pauncho snorting indignantly because Barney was making cracks about hippos in subways. But when they were out of danger, they sat down and wiped the sweat off.

Barney said, 'Do you think - ?' He stopped. Of course, Doc Caliban had no way of knowing whether or not there would be more such traps ahead. And they now had no rifles. They could go back and pick some more up. But, if they were being observed, the block could be withdrawn as soon as they went past the wedged rifles. And it could then be slammed in again with an excellent chance of catching them.

Barney and Pauncho had both thought of this, because Pauncho said, ‘I’ll stay there holding on to a rifle and make sure that if the stone's moved, I'll be there to catch it again.'

'Three rifles were strong enough to withstand it,' Doc said. 'I don't know that just one would do it.'

'They're close enough I could reach out and grab two,' Pauncho said. 'And Barney could hold the other.'

Doc looked at the block. This one was so much closer to the ceiling that crawling on its top was ruled out. It was as long as the other, and it had slid out when the three were halfway along its length.

'No,' Doc said. 'It could be withdrawn and slid out before we could reach the rifles. There's nothing to do except go ahead.'

Barney and Pauncho looked dismal. Doc Caliban kept his face expressionless. It hurt him to see them express any kind of faint-heartedness or lack of faith in him. Yet his reaction was illogical whereas theirs was founded on a realistic attitude. They certainly were not cowards or easily downcast. His little experience with them had convinced him of that. Moreover, they had fought together in the worst of the Korean fighting, had escaped together from a Chinese prisoner-of-war camp, and both had won many medals for valour (though none for good conduct). After the war they had returned to school to get their higher degrees. And they had formed a business which had taken them into South America, where they had been captured by bandits and had again escaped. They did not lack courage or resourcefulness.