'Is Za so weak that his woman must speak for him?'

'I say it was Old Mother! She showed them another way from the cave of skulls. She will tell you!'

'The old woman speaks no more,' said Kal. 'She does not say she did this, or did that. Old Mother is dead. Za killed her.'

Kal stooped and snatched the stone knife from beneath Za's skins. 'See! Here is the knife Za killed her with!'

There was a rumble of anger from the Tribe.

Suddenly, the Doctor spoke, his voice loud and commanding.

'The knife has no blood on it.'

Everyone stared at the knife. As the Doctor had said, the stone blade was clean.

Kal looked down at the knife in his hand. 'It is a bad knife! It does not show the things it has done.'

The Doctor laughed scornfully. 'It is a finer knife than yours.'

Kal hurled the knife to the ground. 'I say it is a bad knife.'

The Doctor pointed to the knife where it lay on the ground. 'I say this is a fine knife. It can cut and it can stab. It is a knife for a chief. I have never seen a better knife than this.'

'I will show you one!' Kal snatched out his own knife and held it out. It was a fine knife indeed - and the blade was caked with dried blood.

The Doctor's voice rang out. 'Your knife shows the things that it has done. Your knife has blood on it! Who killed the old woman?'

Za raised himself on one elbow. 'I did not kill her.' He struggled to his feet, and stood swaying to and fro a moment. 'Kal killed her!'

'The old woman set the strangers free,' screamed Kal. 'She showed the the way to leave the cave of skulls without moving the great stone. I, Kal, killed her!'

The Doctor stepped forward, spreading out his hands. In some extraordinary way he was dominating the whole savage gathering. 'Is this your strong leader? One who kills your old women in his fury?

He is a bad leader. He will kill you all when he is angry.' He leaned across to Ian and spoke in his normal voice. 'Follow my example, young man!'

The Doctor bent and picked up a stone and hurled it at Kal.

'Drive him out!'

Kal gave a roar of anger, and brandished his knife.

Ian, too, grabbed a stone and flung it at Kal.

'Yes, drive him out. He kills old women!'

Hur snatched up a stone and threw it. 'Kal is evil! Drive him out!'

Reeling a little, Za bent and picked up a stone. 'Drive him out!'

Suddenly, everyone was picking up stones and throwing them.

Kal stood helplessly for a moment in the hail of missiles, and then turned and fled into the darkness.

'Well done, Doctor,' whispered Barbara.

The Doctor gave her a self-satisfied smirk. 'Child's play, my dear. These people are just as susceptible to mass hysteria as the people of your own time.'

The victory over Kal seemed to have given Za back his strength. 'Kal is no longer of this Tribe,' he shouted. 'We will watch for him. If he comes back we will kill him.'

Hur said anxiously, 'Kal is strong, and you are weak from your wounds. He will kill you if he can.'

'Remember,' said Ian. 'Kal is not stronger than the whole Tribe.'

Za looked hard at Ian, as if struggling to understand the new idea. At last he nodded, pleased. 'We will all fight Kal, if he comes back.' Za pointed to one of the young warriors. 'You will watch for him!'

The warrior nodded and moved away from the cave, looking in the direction in which Kal had fled.

His authority restored, Za turned to the other warriors. 'Return the prisoners to the cave of skulls.'

Ian sprang forward. 'No, Za. I am your friend. Take us to the place where Kal found us, and I will make fire for you.'

Za ignored him, selecting other Tribesmen. 'We shall use the great stone to close the cave again, and you will stand by another place that I will show you.' He raised his voice. 'Take them away!'

Tribesmen descended on the Doctor, Susan, Ian and Barbara, gripping their arms.

'Don't struggle,' called the Doctor. Rather unnecessarily, thought Ian, since struggle against their brutish captors would have been quite useless.

They were dragged away.

Za watched them thrust into the cave and saw the stone rolled tight against the entrance. He turned to a warrior and led him to a clump of bushes not far from the cave. 'The other way out of the cave leads here. If you see them come out - kill them.'

In the cave of skulls, the Doctor and his companions stood looking around them in despair. A hazardous escape, a long and dangerous journey, and now they were back where they had started, in this terrible cave with its piles of rotting skulls and its cloying stench of death.

Barbara saw the body of Old Mother at the back of the cave and gave a scream of horror. 'This place is evil,' she sobbed. 'Evil!'

'At least they haven't tied our hands this time. Well, Doctor, what do we do now? Got any bright ideas?'

The Doctor stood lost in thought, rubbing his chin. He looked up. 'As a matter of fact, young man - I have!'

Za and Hur were talking, standing by the flat stone in front of the great cave. Za was almost himself again by now. The claw marks on his arm and shoulder had stopped bleeding, and he was able to ignore them. His mind was full of questions.

'Tell me what happened after I fought with the beast in the forest.'

'You were stronger than the beast,' said Hur proudly. 'It took away your axe-head in its side. You lay on the earth, covered with the blood of the beast. I thought you were dead.'

'And the strangers? Tell me what they did!'

'The young man of their tribe came towards you. He did not kill you. He told me his name.'

'His name?'

'He said his name was Friend.'

'They must have come from the other side of the mountains,'

said Za thoughtfully.

'But nothing lives there.'

'So we thought. But I see that we were wrong. This new tribe comes from there. Tell me more of what happened. Tell me what the strangers did next.'

Hur frowned, struggling to remember. 'I did not understand them, Za. They moved slowly, and their faces were not fierce. They cared for your wounds, and carried you on their skins, as a mother carries her baby. Why did they not kill us, Za? We were their enemies. We made them captive.'

Za shrugged helplessly. 'They are a new tribe. They are not like us. Not like Kal's tribe either. Their minds hold strange thoughts.

The young one, the one called Friend, spoke strange words to us.'

'I do not remember.'

Za frowned with the effort of recollection. 'He said, "Kal is not stronger than the whole Tribe."'

'I do not understand.'

'It is a new thought,' said Za. 'But I understand. Except for me, Kal is the strongest warrior in the whole Tribe. And I was weak. But the whole Tribe drove Kal away with the stones. Even the old men and women, even the children, were stronger than Kal, together.'

Za wrestled with this new concept of co-operation. 'The whole Tribe can gather more fruit than one. The whole Tribe can kill the beasts in the forest, where just one hunter would die.'

'Their minds are not like ours,' agreed Hur. 'Perhaps they come from Orb. That is what the old men are saying. They say we must return them to Orb in sacrifice.'

'No, they come from a tribe across the mountains. They can make fire, but they do not want to tell us, because our Tribe would become as strong as theirs.'

'What will you do with the strangers, Za? Will you kill them?'

Za shook his head. 'Your father, Horg, says that the leader must know how to make fire. I do not wish to be driven into the forest, like Kal. I must learn to make fire. The strangers must teach me. Otherwise they will die.'