'No, no. Can't do that. Work to do. Got to help the Doctor...' Suddenly he gripped her arm. 'Victoria, don't move. There's a Yeti-'

Victoria sighed. 'I know, Professor, it brought us here.'

Taking her by the hand, Travers began backing slowly away. The Yeti didn't move. They turned to run, and found themselves facing the second Yeti. It growled menacingly.

Travers and Victoria moved back to the bench. Hopelessly, they sat down to wait.

The sphere was thudding against the laboratory door, as if trying to make a hole in it. Already the wood was beginning to splinter. 'It'll smash through in a minute,' said Anne.

The Doctor made a last adjustment to the control device. In its final form it was a small black box packed with electronics, controls set into the lid. The Doctor snapped the lid shut, 'Let's see if it works.'

He adjusted the controls. The sphere continued to slam against the door. Anne looked worried, 'Is it on full power?'

The Doctor nodded, readjusting the controls. Still the sphere thudded mindlessly into the door. Anne shook her head. 'It's no good. We've failed.'

The Doctor moved slowly around the room, holding the control box in different positions. He came nearer and nearer the sphere. When he was little more than a yard away, the sphere stopped moving. 'Ah-ha!' he said triumphantly. 'It does does work-but only at very short range. Better than nothing, though.' work-but only at very short range. Better than nothing, though.'

'What next, Doctor?'

The Doctor rubbed his chin. 'We can stop a Yeti with this thing-but that isn't enough. We've got to reprogramme the sphere to obey our commands. How long have we got?'

Anne looked at her watch. 'About half-an-hour!'

Victoria and Travers were talking in low whispers.

'You're sure Anne is all right?' Travers asked anxiously.

Victoria nodded. 'She's with the Doctor. Don't worry, I'm sure they'll find the answer.' Travers was still very confused and Victoria felt she had to keep his spirits up.

Strangely enough this had the effect of making her feel better herself.

There came a bleeping sound, and the nearest Yeti moved away down the platform, disappearing into the tunnel.

Travers stared after it puzzled, but Victoria was looking in the other direction. She pulled at the Professor's sleeve. 'Look!'

Sergeant Arnold was stumbling along the track; his forehead was gashed, his uniform tattered. He moved nearer. The remaining Yeti seemed oblivious of his presence.

Travers hissed, 'Arnold! Yeti! Hide!' He pointed to the nearby Yeti. A look of understanding came over Arnold's face and he ducked below the platform. Travers and Victoria edged slowly towards him, taking care not to alarm the Yeti.

'Arnold!' muttered Travers again. 'Can you make it back to H.Q.?'

'Think so, sir.' Arnold's voice was faint below them.

'Get back and tell the Doctor where we are.' 'What about you two?'

'We can't move, or the Yeti will attack. But it's guarding us-it doesn't know about you. Off you go, man.'

Arnold crept along the track and disappeared into the tunnel.

Jamie and the Colonel moved cautiously along.

Suddenly Jamie stopped. 'Look here!' He picked up a sc.r.a.p of white linen, edged with lace. 'Victoria's hand-kerchief. At least we know we're on the right track.' The Colonel said, 'Listen!'

They could hear the sound of footsteps stumbling towards them.

'Donna' sound sound like a Yeti; whispered Jamie. It wasn't. like a Yeti; whispered Jamie. It wasn't.

Sergeant Arnold stumbled into view. He saw the Colonel and tried to come to attention, but he reeled and almost fell.

Lethbridge-Stewart caught hold of him.

'Sorry about this, sir,' Arnold muttered faintly.

'What happened to you, Sergeant? We'd given you up for dead.'

'Don't really know, sir. I was pushing the trolley into the Web and I blacked out. When I came to, I was wandering around the tunnels. Listen, sir, I've seen Victoria and Professor Travers.'

'Where are they?' asked Jamie excitedly.

Arnold gestured behind him..'Just back there...

Piccadilly. Yeti was guarding them. They said get back to H.Q.... warn Doctor...'

'And that's exactly what we'll do,' decided Lethbridge-Stewart. 'Come on, Jamie, at least we know where Victoria is now. There's nothing we can do till the Doctor gets his box of tricks working.'

Supporting Arnold between them, they began to move slowly back the way they had come.

Private Evans sat in the empty Operations Room, rifle across his knees. He was uncomfortably aware that he was one of the few remaining survivors among all the soldiers who had manned the Fortress. He was wondering how long it would be before his luck ran out. When the little silver sphere rolled through the door and across the floor towards him, he jumped straight on to his chair, like a girl frightened by a mouse. Lifting his rifle he took aim at the sphere.

The Doctor appeared. 'No, don't shoot!' He looked at the sphere and said, 'Stop!' To Evans's astonishment, the sphere obeyed. 'Sorry if it frightened you,' the Doctor apologised.

Evans climbed down from the chair. 'I wasn't frightened frightened...

Just got up there to take a better aim, see? How did you make it stop?'

'I told it to.'

Evans leaned forward. 'Here, ball, you go back where you came from.'

The sphere didn't move.

The Doctor chuckled and spoke into a small radio-microphone slung round his neck. 'Move back. Stop. Move left. Stop. Now right... Stop.' The sphere obeyed each command. Anne Travers joined the Doctor.

'How about that?' she said proudly.

Evans looked dubious. 'It'd make a smashing toy-but how's it going to help us?'

'Don't you see,' said the Doctor. 'Once we get it inside a Yeti, the creature will obey our commands.'

Evans paled. 'Just how do you get it inside a Yeti?'

'We're going to Warren Street to look for one now.

Coming?'

Evans shook his head. 'Me go near one of them things? I may be stupid but I'm not that daft.'

'All right,' said Anne, 'we'll do it on our own, won't we, Doctor?' She held up her hand as the Doctor started to protest. 'It's no use arguing-I'm coming with you.'

Travers and Victoria heard bleeping as the second Yeti returned along the tunnel. It came directly towards them and the other Yeti joined it. Victoria realised they were being shepherded along the platform. 'Where are they taking us?'

she whispered nervously.

'I've no idea. Don't worry, we'll be all right.' Travers tried to sound optimistic-but he didn't really believe what he was saying.

Now alone in the entire Fortress, Private Evans was more nervous than ever. He tried a quick chorus of 'Men of Harlech', but it did little to lift his spirits. He heard the sound of footsteps in the corridor and peeped cautiously out. To his astonishment he saw Jamie, the Colonel and Sergeant Arnold.

'Where's the Doctoor?' snapped Lethbridge-Stewart. 'We looked in the laboratory but he wasn't there.'

Evans was staring transfixed at the Sergeant. 'But...

but...'

Arnold, who seemed to be recovering rapidly, growled, 'Don't stand there bleating like a Welsh baa-lamb, Evans, answer the Colonel.'

'The Doctor and Miss Travers have gone back into the tunnels, sir,' said Evans nervously. 'Warren Street, they said'

'What the blazes for?'

'Said they wanted to catch a Yeti, sir.'

Lethbridge-Stewart shook his head disbelievingly. 'All right, Private Evans. Get the first-aid box over there and put a dressing on the Sergeant's head.'

'Yessir!' Evans ran to the laboratory, fetched the first-aid box and began bandaging Arnold's head with considerably more enthusiasm than skill. Lethbridge-Stewart looked on, wondering what on earth he was going to do next.

Jamie was looking at the indicator map. Suddenly the Warren Street light began to flicker. 'The Web's moving again. We'd better warn the Doctor.'

The Colonel turned to Evans. 'You stay here and finish what you're doing. We'll be back as soon as we can.'

Anne Travers and the Doctor rounded a bend in the tunnel and found their way blocked by a solid wall of the Web. The Doctor sighed. 'No good. we'll have to go back and find another way...'

They turned and suddenly froze-a Yeti was moving down the tunnel towards them. 'We're trapped,' whispered Anne.

The Doctor shook his head. 'Not a bit of it. We wanted a Yeti and now we've found one. Pa.s.s me the control box, Anne.'

She stared at him. 'You were carrying it, Doctor!'

'Oh was I?' The Doctor started feeling in his capacious pockets.

The Yeti moved steadily nearer.

The Doctor produced the sphere and pa.s.sed it to Anne.

'Here, hold this.' He went on searching.

Anne shrank back as the Yeti came closer. It had spotted them now. The red eyes glared menacingly, and it gave a savage howl. Now almost upon them, it raised its paw to strike. The Doctor produced the box from his pocket and touched the controls. The Yeti froze, one arm still upraised.

Anne gasped with relief. 'I know it only works at close range, Doctor, but really...'

The Doctor chuckled. 'You weren't worried, were you?

Here, take this, and give me the sphere.' He pa.s.sed Anne the control box, took the sphere from her and opened the flap in the Yeti's chest. Quickly he took out the sphere already there and inserted his own reprogrammed one in its place. He stepped back and spoke into the radio-microphone slung round his neck. 'Now then, you-turn round.' For a moment nothing happened. Then, slowly, the Yeti turned.