Close behind her came Ian and Barbara.

Ian leaped forward and grappled with Kal. For a moment they struggled furiously. Another Tribesman raised a stone axe above Ian's head. He was about to strike when the Doctor shouted commandingly, 'Stop! If he dies, there will be no fire!'

The Tribesman halted the downward movement of the club, and looked inquiringly at Za. 'Kill them,' shrieked Old Mother.

Za considered. 'No. We do not kill them.'

'They are enemies. They must die!'

Impressively, Za said, 'When Orb brings the fire to the sky, let him look down on them as his sacrifices. That is the time they shall die - and Orb will be pleased with us, and give us fire. Put them in the cave of skulls.'

The four strangers were dragged off struggling. Kal looked thoughtfully at Za, and slipped away.

Horg put his hand on Hur's shoulder to draw her away, but Za stepped down from the rock, and took Hur's arm. 'The woman is mine.'

'My daughter is for the leader of the Tribe.'

'Yes,' said Za. 'I am leader. The woman is mine.'

Horg sighed. 'I do not like what has happened. I do not understand.'

'Old men never like new things to happen.'

'In the time of your father, I was his chief warrior. He was a great leader of many men.'

'Yes, many men,' repeated Za bitterly. 'They all died when Orb left the skies and the great cold was on the ground. Now Orb will give me fire again. To me, not you. Just as you will give me Hur.'

Consolingly, Hur said, 'Za, too, will be a great leader of many men. If you give me to him, Za will remember, and always give you meat.'

Accepting the inevitable, Horg bowed his head and moved away.

Old Mother stared broodingly at Za. 'There were leaders before there was fire,' she muttered. 'Fire angers the gods. Fire will kill us all in the end. You should have killed the four strangers. Kill them!'

Za shook his head, looking into the gathering darkness. 'It shall be as I have said. We wait until Orb shines again in the sky. Then they will die.'

Arms and legs trussed like captured animals, Ian, Barbara, the Doctor and Susan lay in a smaller cave, just behind the main one.

After binding their arms and legs, their captors had thrown them into the cave and retreated hastily, almost as if they were afraid to stay, rolling a great stone to block the door.

The cave was small and dark, and it stank of death. There were skulls everywhere, arranged in pyramids on the ground.

'Are you all right?' gasped Ian. 'They didn't hurt you?'

'No, I'm all right.' Barbara's voice was trembling. 'I'm frightened, Ian.'

Ian could offer little consolation. 'Try and hang on. We'll get out of this somehow.'

There was hysteria in Barbara's voice. 'How? How are we going to get out of it?'

'We shall need to be cunning,' said the Doctor thoughtfully. He seemed remarkably spry after his ordeal, already he was busy struggling with his bonds. After a moment he said, 'I hope you can get yourself free, Mr Chesterton - because I can't.' He looked at the others. 'I'm sorry. All this is my fault. I'm desperately sorry.'

'Grandfather, no,' sobbed Susan. 'We'll find a way out. You mustn't blame yourself.'

('Why not,' thought Ian sourly. 'The old fool's quite right, it is all his fault!')

The Doctor looked at the pile of skulls in front of him. He shoved one towards Ian with his feet. 'Look at that, young man!'

Clumsily Ian picked it up. (Luckily, their hands had been tied in front of them.) 'It's a skull.' He tossed it aside, leaned forward and picked another from the pile, and then another examining them carefully. 'They're all the same,' he whispered. 'The crowns have been split open!'

7

The Knife

The Tribe was sleeping.

Huddled together for warmth, wrapped in such skins as they possessed, the cave people slept, dreaming of fire, trying to forget the deadly cold that seeped through the caves - the cold that would grow fiercer, stronger, night by night. Unless the fire came back soon, there would come mornings when the weak ones, the women and children and the old would not wake. When the cold was at its fiercest, even strong men died in the night.

Only Old Mother was still awake. Fire leaped in her mind too, but not as a saviour, a protector. To Old Mother fire was an evil demon. Her confused mind associated it with the death of her husband, Gor, and with all the misfortunes that had come upon the Tribe.

The strangers threatened to bring fire. The strangers were evil, too. Old Mother thought for a long time, wondering how she might save the Tribe from the menace of fire. At last she thought of a way.

She rose stealthily, creeping across the silent cave to the place where Za lay sleeping, Hur at his side. Za's precious knife lay close to his outstretched hand. The knife was a long thin sliver of stone, its edge ground sharp. Old Mother reached out for it.

Za twitched and muttered in his sleep, as if suspecting her intention and she drew back her hand. He slept again. Old Mother snatched up the knife, and scuttled away.

Hur watched her through half-open eyes, and wondered what she should do.

Ian was holding his tied hands out before him, stretching his bonds in the hope of slipping free of them, but the strips of rawhide were tough and sinewy, and there was little give.

Susan was searching the floor of the cave for sharp-edged stones. 'Here's another one with a rough edge.' She picked it up and hopped over to Ian, hampered by the fact that both her hands and feet were bound.

Ian took the stone in his own bound hands, and moved over to Barbara who stretched her tied hands flat on the ground. Ian began sawing at the thongs with the stone. 'It's no good the stone's too soft.

The edge keeps crumbling.'

'The whole thing is hopeless,' grumbled the Doctor. 'Even if you could get us free, we'd never manage to move the stone blocking the door.'

Ian raised his head, sniffing. 'There's air coming into this cave from somewhere - somewhere else beside the door, I mean.'

'So there is,' said Barbara. 'I can feel it on my face.'

'It may only be a small opening though. Don't count on it..

'Why not - you obviously are,' muttered the Doctor.

'Of course, I am. Any hope is better than none. It's no good just lying there criticising us. Do something. Help us to get out of here if you're so clever!' Ian tossed the stone aside. 'It's hopeless,' he said, promptly contradicting himself.

'Don't give up, Ian, please,' begged Barbara. 'All right. Come on, Susan, let's look for a better piece of rock.'

The Doctor had been silent since Ian's outburst. For once, he had lost his usual air of complacent superiority. A little sheepishly, he said, 'Don't waste your time with stones. Try one of the shattered skulls. A good sharp piece of bone will be more useful.'

'Good idea,' said Ian. He began rooting in the grisly pile of skulls.

The Doctor seemed quite prepared to take charge again. 'We must concentrate our efforts, young man. We must all take turns in trying to cut your hands free.'

'Surely we ought to get the girls loose -'

'No, no, you first. You're the strongest, you may have to protect us...'

Ian nodded, impressed both by his own responsibility, and by the Doctor's ruthless grasp of priorities. He found a skull that had been split almost in two, with -a satisfyingly sharp edge at the break point. Silently, he handed it to the doctor, and stretched out his bound hands.

The Doctor began sawing at Ian's bonds. For a long time he worked furiously. At last he stopped, gasping with effort. 'Susan, you try for a while. My arms are tired.'