'What happened in there?'Vinson asked.

'Explain later!' grunted the Doctor. 'Keep going!'

They half-ran, half-stumbled onwards, Nyssa hanging between them.

Tegan ran on ahead with the torch, but the stone trunks of the stalagmites were growing dimmer already.

'What's happening to the light?'Vinson asked.

'It's being absorbed,' the Doctor panted. They pushed on into the forest, forced to slow down because of the density of the stalagmites. 'The Dark has come back to life, and it's draining the light away.'

'How?'

'I don't... know!' the Doctor shifted his weight and stepped past another stalact.i.te. 'Some kind of... photon a.s.similation I should think.'

'Let's do the science bit later,' Tegan suggested. 'We have to hurry Doctor. The torch is failing!'

The flash's beam was weakening. What had at first been a brilliant circle of white light was now a dim pool of yellow. 'I don't know how much longer it'll last!'

The Doctor gritted his teeth and pushed on with Vinson's help. They kept grazing their knuckles and cracking their shoulders against the stalagmites, but refused to slow down any more. They could all feel the coldness at their backs, and it was getting colder.

At one point Tegan looked back, to find the forest behind them was lost in darkness. It was a malignant darkness, almost like a vertical wall of black ink spreading through the stalagmites, engulfing them one by one, faster and faster.

And it was gaining on them.

'It's coming!' she yelled.

'I can't see where we're going!' called Vinson. 'It's getting too dark!'

Suddenly they heard the crackling whine of blaster fire: somewhere in the gloom a number of bright energy bolts leapt through the trees.

'My men,' Vinson realised, pausing. 'They're shooting at it.'

The Doctor caught his breath. 'They're wasting their time,' he panted. 'It absorbs light!'

In amongst the trees, lit by the sudden flash and zap of the blaster beams, were a number of the Adamantium Adamantium crewmen. They had stopped and turned to fight the encroaching wall of blackness with the only weapons they had. The blaster bolts plunged into the darkness and faded from view. The swelling shadow didn't even falter in its progress. crewmen. They had stopped and turned to fight the encroaching wall of blackness with the only weapons they had. The blaster bolts plunged into the darkness and faded from view. The swelling shadow didn't even falter in its progress.

'We must keep going,' Tegan urged.

'Fall back!' cried Vinson, desperately signalling to his men. 'They've split up,' the Doctor said. 'They're going to get lost.'

The Dark approached one of the men, who continued to blaze away at it uselessly. The burning glare of his blaster silhouetted him briefly against the blackness and then he disappeared from view. A terrible scream tore through the freezing air.

The other men turned and ran, but it was impossible to gain any speed in the forest. None of them could see clearly enough to dodge past the trees, and within moments they had been overtaken by the blackness. Each let out a horrifying shriek of agony as the darkness swallowed them up.

'Come on!' the Doctor said, picking Nyssa up again. He began to move up the slope, Tegan doing her best with the torch's feeble beam to show the way. Vinson, swearing mightily, brought up the rear.

'It's gaining on us!' Vinson cried.

'It's getting darker!' Tegan sobbed.

The Doctor lifted Nyssa on to his shoulder again and scrambled on.

'Don't stop!'

Suddenly they were out of the stalagmites and into the caves again; the light from the rock-snakes seemed an incongruously bright and cheerful green. There were some more crewmen up ahead, calling for them to hurry. Tegan sprinted towards them, her shoes slipping and sliding on the gla.s.sy rock. The Doctor staggered after her, almost bent double under Nyssa's p.r.o.ne form.

Behind them, Vinson turned and stood in the entrance to the tunnel. He watched the blackness fill the forest cavern and race towards him.

'Vinson!' Tegan screamed as she looked back. 'Hurry!

You'll be killed!' The Doctor collapsed and lay Nyssa on the tunnel floor. Some of the Adamantium men Adamantium men came back to help him pick her up. The Doctor turned around when he heard Tegan shouting. came back to help him pick her up. The Doctor turned around when he heard Tegan shouting.

Vinson, lit green by the glow-snakes and framed against the Dark, stood up straight and aimed his blaster in a double-handed grip. 'This is set to burn, you b.a.s.t.a.r.d,' he said, and pulled the trigger.

Brilliant red light burst from the gun and vanished into the blackness.

The terrible shadow suddenly filled the tunnel entrance and swept over Vinson where he stood. Wraiths of darkness swirled and dashed around him, lifting him off his feet and shaking him like a rat. As he faded from view, Tegan almost thought she saw him turn transparent, as if she had glimpsed his bones and internal organs for just the briefest moment.

Then there was nothing but the darkness and a blood-curdling shriek that seemed to linger in her head for far longer than she actually heard it.

'Quickly,' she heard the Doctor shout, feeling him grab her arm and pull her back. But she kept her eyes on the Dark: it seemed as though pieces of it were breaking away, solid shadows that rushed on ahead of the main body of the blackness, chasing after them. A dreadful, bloodfreezing howl built up in the tunnel and a great blast of cold air heralded the approach of the shadow wraiths. Tegan turned and ran for her life.

The Doctor held onto Tegan's hand, pulling her after him.

Together they dashed back up the tunnel. Tegan had no idea how far away the entrance to the laboratory complex was, but she knew she couldn't run much further. Her heart was grinding painfully in her chest and she could feel herself weakening.

'Come on!' the Doctor insisted, yanking her after him, harder, faster. His voice was ragged with the exertion, 'Keep 'Keep going!' going!'

She could feel the icy breath of the Dark on her skin, hear the scream of its wraiths as they swept up the tunnel behind them. The darkness began to close in, the cave walls growing dimmer with every step.

Suddenly there was a bright light ahead of them: the door to the stasis-tank chamber. With a final, lung-bursting heave they shot through the doorway and sprinted up the steps that lead to the main lab. There they collided with a small group of Adamantium Adamantium crewmen. crewmen.

'Close the door!' cried the Doctor from the floor.

Someone hit the switch and the big metal door hissed shut.

Something ma.s.sive struck the other side with a huge clang and the door shook in its frame. Everyone in the lab flinched.

Tegan lay on her back, breathing so hard she thought she would faint. faint.

The Doctor clambered to his feet and moved back to the door. As he approached it, there was another huge clang clang as something pounded against the other side. as something pounded against the other side.

The Doctor stepped back. 'Well, it seems to be sealed...

for the moment.

The door was struck again with a terrible boom. boom.

'Can it get through?' one of the crewmen asked shakily.

'Given time, undoubtedly; the Doctor replied. He was still breathing heavily.

'How much time?'

The door boomed again and vibrated with the impact.

The Doctor licked his dry lips. 'I don't know. A couple of hours? A few minutes? It's impossible to tell.'

'What is it?' asked another man.

'If it gets through that door, it'll be the end of us all,' the Doctor told him bleakly. 'We have to get away from here and quickly.' He headed for the exit. 'If we can get back to the Adamantium Adamantium in time, we may be able to get you all off this moon.' in time, we may be able to get you all off this moon.'

The door shook again, and dust dropped from the ceiling.

Then it shook again. And again. Each impact reverberated around the lab with a heart-stopping clang. clang.

Boom! Suddenly a dent appeared in the metal. Suddenly a dent appeared in the metal. Boom! Boom!

Then another dent.

It appears we haven't a moment to lose,' said the Doctor.

'Let's go.' He helped Tegan to her feet and began to usher the Adamantium crewmen from the room. Behind them, the door shook again and distorted visibly. As they left the lab complex, they all heard the repet.i.tive clang of something hurling itself against the metal with terrible ferocity, harder and harder, and faster and faster.

Those that survived returned to the Adamantium in a state of shock and despair. Many of the men had lost friends and comrades, and few of them really understood how.

The Doctor and Tegan quickly caught up with the crewmen who had taken Nyssa back to the ship.

'How is she?' Tegan asked.

Nyssa looked deathly pale. There was no trace of the black bile they had seen in the crypt, however.

The Doctor examined her quickly on the medical couch.

He checked her pulse and lifted each eyelid. 'She's all right,'

he said at last, although his voice sounded quiet and strained. 'But she's lucky to be alive.'

He leant forward on the bed and hung his head. All his strength and vitality seemed to have been drained away. 'If anything had happened down there...' he began. 'If she'd... If I'd let anything happen happen to her...' to her...'

Tegan reached out and touched his hand. It was cold.

'It's all right, Doctor. She's going to be OK. You saved her.'

He looked up at her. His eyes looked as blue as snow shadow. 'No I didn't. I left her to the Dark and when it had finished with her, when it had discarded discarded her... I took back what was left. her... I took back what was left.

'You're punishing yourself. The important thing is that she's all right, that she's free of it now.'

'But at what cost? The Dark is free. I risked her life for nothing!' He was breathing heavily. 'The Dark was in control all the time, Tegan. It used her and I knew it was using her.

But I was powerless to stop it.

'That's not your fault.'

'But the fact is that the Dark managed to do all that even before before it was fully resurrected, Tegan. Don't you see what that means? It's been brought back to life: it's even more powerful now. How am I going to stop it?' it was fully resurrected, Tegan. Don't you see what that means? It's been brought back to life: it's even more powerful now. How am I going to stop it?'

'You'll think of something.'

The Doctor shook his head. 'We have to see Lawrence.

He has to blast off now, while he still can. At least that way we might save the lives of those that still remain.'

The Doctor and Tegan headed straight for the bridge, where they found Captain Lawrence and Jyl Stoker. One look at the Doctor's sombre expression told Lawrence all he needed to know.

'We were too late,' the Doctor told him, and quickly gave an account of what had happened. 'You have to prepare for take-off immediately, Captain. It's your only chance.'

Lawrence looked impa.s.sive. 'I see. What about Cadwell?'

'I don't know.' The Doctor slumped into a vacant chair and gingerly felt the blood that had dried around his nose. 'He got out of the crypt. I think.

I didn't see him after that. Presumably the Dark got him.'

And good riddance, if you ask me,' Tegan said bitterly. 'It was all Cadwell's fault anyway: somehow he managed to resurrect the Dark.

There was a dry chuckle from the entrance to the bridge.

'Is that what you think?'