The mouthless man nodded vigorously. 'See?' said the Doctor. He checked the controls again. 'Yes, see? Our friend here has sent an alert up to the captain to tell him the drive has stalled. But there's not been an answer, so presumably it hasn't got through. But at least everyone knows their place! The lowest ranks literally can't speak back to their superiors, and now that's going to cost everyone their lives.'

'It's that bad?' said Martha.

'Any effort to engage the ship with the drive stalled like this and it's likely to explode. It's really just a matter of time.'

'We have to do something!'

The Doctor reached out for her hand, gazed deep into her eyes. 'Martha, we can't. Not when it changes history.'

He gazed at her levelly with his dark and twinkling eyes. But Martha refused to look away; this was too important. She was a proper doctor, even if he wasn't. She had a duty to stop and help. And sometimes the Doctor needed her to remind him when he was wrong.

'All right,' he said wearily. 'We'll pop upstairs. I'll have a word with the captain. A few quick pointers and then we'll let them get on their way.'

Martha grinned. 'Great!' she said. 'You know it's the right thing to do.'

'I'm not sure I do, but anyway.' He turned to the mouthless man. 'Sorry about all that yammering there,' he said. 'Just needed to parley a plan. Anyway, we're going to get this sorted out for you. Which way to the exit?'

The mouthless man again gestured wildly, using both arms this time. He seemed unable to make any noise at all, and the worst thing about it was his own frustration at not being understood.

'Maybe if you just lead us,' said Martha, trying to make it sound kind.

The mouthless man nodded. They followed him back down the alleyway between the machines, and round past the TARDIS. Set into the wall was what looked like a shower – a person-sized booth with a glass door.

'Ooh!' said the Doctor, dashing over. 'I've not seen these in years! One-way transmat up to the bridge.' He turned back to the mouthless man. 'Is it a bridge, or is it more of a cockpit?' The mouthless man shrugged, unable to reply. 'Oh, never mind,' said the Doctor, turning back to the machine. 'Martha, this is brilliant. You step inside, press the button, and ping! you're in a booth just like it at the far end of the ship.'

'It's a teleporter, yeah?' said Martha. 'Like in Star Trek.'

'Well, not exactly like Star Trek,' said the Doctor, busy trying to get the door open. It wouldn't budge. 'For one thing, it'll make a different noise. Anyway, this is just for getting upstairs without all that boring business of walking. It's cheating, if you ask me.'

'Not if you can't get into it,' said Martha.

'It's stuck!' said the Doctor, turning to the mouthless man. 'I wondered why you'd not just gone to see the captain yourself. Something must be coming through the other way. Something really, really slow. It's like being on dial-up!'

'When were you ever on dial-up?' asked Martha.

'I read about it,' said the Doctor. 'Well,' he said to the mouthless man. 'That way's blocked for the moment. Probably with some movie about a cat on a skateboard. So we'll go see your captain on Shanks's pony.'

The mouthless man stared dumbly at him.

'He means,' said Martha, 'we're going to have to walk. Why can't you talk normally?'

'What?' said the Doctor. 'And be just like everybody else?'

The mouthless man led them back round the TARDIS and then off to one side. They followed a narrow passageway to a thickly reinforced door. A complicated sequence of different handles and locks allowed the mouthless man to open it.

Martha had expected to see the plush fittings of a luxury ship. Yet the way was barred by a strange, pale skin of material, like a kind of fungus. It totally blocked the door. The mouthless man again gestured emphatically; it was this obstacle he'd tried to explain.

'Somebody really doesn't want us getting out of here,' said the Doctor. 'Cor, this is a bit unusual!' He put his hand out and stroked the pale surface. 'Feels like cold scrambled egg!'

'Do you know what it is?' asked Martha.

'Oh yeah,' said the Doctor. 'Seen this before. The TARDIS can get clogged with the stuff.'

'It's some sort of time fungus, then?'

'That's the technical name for it, obviously,' laughed the Doctor. 'You get it where time doesn't quite meet up. Time, right, comes in chunks.'

'Chunks?' said Martha.

'Yeah,' said the Doctor. 'Really! But "chunks" sounds silly, so your lot use the Greek word quanta.'

'Like quantum mechanics,' said Martha.

'That's it exactly,' said the Doctor. 'So it comes in chunks. And this stuff lives in the gaps between moments, between the Planck units. Ship like this, it's going to make a lot of it. But it's weird to see it inside the ship.'

'It's some kind of weed?'

'Nothing like that. Something much, much, much more peculiar. You imagine you're in a lift, going between different floors.'

'This is another analogy, is it?' said Martha.

'Yes, it's another analogy. It's the only way you'll understand it! Right, you're in this lift. But it's one of those old warehouse lifts that doesn't have any doors.'

'So you see the floors going by.'

'Yeah, that's it. And when you're between floors?'

'Uh . . . Well, you see the bits in between the floors. Concrete and stuff.'

'Right! Now what's happened is that our little bump has stopped the ship between different floors. Only some of the ship's on one floor, and some of it's on another.'

'So this is the concrete between floors?' Martha rubbed her hand against the pale substance. Yes, it was soft and rubbery, just like cold scrambled egg.

'Yeah,' said the Doctor. 'Normally no one sees it. Which is good 'cos it doesn't half make a mess.'

'So we can't get through it, then?'

The Doctor laughed. 'What?' he said. 'When I've got this?' And he brandished his sonic screwdriver. 'I just need setting twenty-eight.' He waved the sonic screwdriver at the scrambled egg material. After a few seconds he poked the eggy skin with his finger. His fingertip broke through the surface.

'See?' he said. You just step through sharpish before it hardens again.'

'It's that simple?' said Martha, not wholly convinced.

'Trust me,' said the Doctor.

She laughed. 'You know you only say that when it's really bad.'

'Do you want me to go first?'

That was enough to decide her. 'No,' she said. 'You can cover my back.'

THREE

It took a while for the sonic screwdriver to soften the stuff blocking the door. Martha had time for another cup of tea and a one-sided chat with the mouthless man in Bermuda shorts and leather apron. It seemed brilliant at first that she could tell him anything and all he could do was listen. But the unfairness of it soon got to her. She had told him all about her family, and Dad and Annalise, and she didn't know one tiny thing about the mouthless man himself. Did he like his job? Did he have someone who loved him? He just watched her, nodding encouragingly but not even able to smile.

Again she felt that fierce determination to do something for these people. Somehow, she and the Doctor were going to make things better.

'Right,' said the Doctor, prodding the scrambled egg with his fingers. Think that's soft and squidgy.'

'How thick is it?' asked Martha, suddenly rather nervous.

'Er . . . No idea,' said the Doctor. 'I've never done this before. Can't be too thick if it resonates so quickly. But who knows?'

That's not exactly reassuring.'

'No? Well, I'll be along right after you. We can compare notes on the other side.'