Rachel looked down. 'That book?' she said.

Marnal's eyes glinted. 'If you clear a s.p.a.ce on the dining table, I'll show you.'

After half an hour Marnal had a.s.sembled all sorts of things from the garage and various piles of junk around the house. A big gla.s.s bottle from a home-brewing kit, an old portable television, what looked like a section from a recording studio's mixing desk. After about an hour's work connecting them up with cables to a row of smelly old car batteries, he stood back.

To Rachel's amazement, the inside of the gla.s.s bottle had gone dark, then tiny bright dots had started to resolve.

'Galaxies,' Marnal a.s.sured her. He was twiddling with the mixing-desk controls, checking the television screen, which was full of what looked like Greek symbols.

'Greek?' she asked.

He smiled condescendingly. 'No, these are letters of the Gallifreyan omega-bet.'

'Which is like an alphabet, but superior?'

'The last word, you might say.'

Rachel peered into the bottle. Wherever she looked, she was able to focus in and in and in and in and in. So the galaxies became stars, became planets, became patches of land. It made her eyes go funny, and she had to blink and start again a couple of times. She saw something that looked like the moon, only the rocks were more jagged and there was a strange purple sky. Things that looked like woodlice were burying themselves in the soft sand.

Aliens, she realised. She was looking at alien life forms.

Then the contents of the bottle faded away, and she found herself staring at Marnal's face on the other side, distorted in the clear, curved gla.s.s. He was holding the power cable, which he'd unplugged from the car batteries.

'These will go flat in a matter of minutes. I need a better power supply,' he told her. 'I'll construct a cold-fusion reactor. Shouldn't take long.'

'But no one knows how to do that,' Rachel said.

'No one on Earth. It's child's play to my people. Your human children rub sticks together to make fire?'

24.'I was a Girl Guide, but I was useless at all that.'

Marnal gave her a forgiving smile. 'Well, fusion is just a simple matter of rubbing helium nuclei together to make energy.'

'And it's safe?'

'Oh yes. Completely clean.'

'You could solve loads of problems on Earth,' she told him. 'The energy crisis, the dependence on fossil fuels, air pollution, cheap s.p.a.ce travel. . . '

'Yes, but there are more pressing matters. I have one last car battery.'

He connected it up and started scanning star systems.

'Now, it's towards the galactic core, it should be around. . . ' He paused. 'I don't understand. It's gone.'

'What do you mean gone?'

'If I could answer that question. . . I can't find Gallifrey. I can't even see Kasterborous. Anywhere in s.p.a.ce or time.'

'You don't want to go to a genuine Roman orgy?' the Doctor said, astonished.

They were standing in the marketplace. The farmers and merchants had all gone home for the night, cleared their stalls and tied back the bright awnings.

The fountain was still playing, though. A beggar was sitting at it, dipping a cup into its trough for a drink. A small statue of Ceres looked over the scene.

'No,' said Fitz, apparently cheerfully. 'You do that, we'll follow the old washerwoman.'

The Doctor looked at him suspiciously. 'Not like you to turn down wine, women and song. Wait, are you. . . ?'

Without warning, he grabbed Fitz's head and stared into his eyes, as though he was trying to get a look at his brain.

'Gerroff!' Fitz complained, shaking him away. 'No, I admit it's not like me.

But on this occasion I mean. . . you're OK going instead?'

The Doctor nodded, and checked his toga one last time. 'Needs must. Good luck, the pair of you.'

He hurried off and disappeared between two columns of the colonnade.

It was a pleasant Italian evening, so a little too warm for Fitz and Trix.

'I'm very proud of you,' Trix told Fitz as they made their way back to the villa they'd cased earlier that afternoon.

'You owe me, that's all I'm saying.'

Trix kissed him on the cheek. 'I'll repay you with interest.' He blushed in a very endearing way.

'So, what do you think's up?'

'That face-grabbing was a clue,' Fitz said. 'Someone's in disguise. And we're in history, so I'm guessing the baddy is trying to alter the time line or something like that. Mount Vesuvius is probably involved too.'

25.Trix smiled sweetly. 'Mount Vesuvius? Fiver?'

'As ever.'

They took up a position at the back of the villa.

'You're thirty-five quid down so far,' she pointed out, 'after seven bets.'

'I'm due for a change of luck, then.'

'Look!'

Trix pulled Fitz out of sight as one of the back doors opened. An old crone shuffled out, carrying a basket of clothes and linen that was almost the same size as she was. Trix and Fitz followed her a little way to where she had a mule tethered. With a bit of difficulty, the old woman attached the basket to the mule's saddle. She slapped its shoulder and it clip-clopped away, with the old woman half-guiding it, half-led by it.

Trix followed, slipping from shadow to shadow. Fitz wasn't far behind.

'I'm getting too old for this,' he said.

'Oh come on, it's fun.'

'Hey, I'm not denying that.'

The washerwoman was a hundred yards away and about to disappear down an alleyway with her mule. They hurried to catch up with her.

They were back in the marketplace. The old woman was unloading her basket, and looked befuddled by the attention she was getting from Trix and Fitz. The mule was drinking from the trough of the fountain, presumably taking the opportunity before the washing went in.

'Get her!' Trix shouted.

Fitz grabbed the washerwoman's arms, and held her in place.

The woman didn't say a word; she just looked shocked.

'I know your secret,' Trix said, confronting her. 'You're no washerwoman.

You're a spy.'

'She's not a washerwoman?' Fitz asked, one eye on the basket of washing.

Trix grabbed the washerwoman's face. 'She is not even a she, Fitz. This is a man, one with an obviously false nose.'

The nose stayed in place, despite Trix's best efforts. The washerwoman yelped and whined, finally slapping Trix hard on the face and running off.

'd.a.m.n. She looked so butch. You'd think I would know a disguise when I saw one. Could have sworn it.'

'No,' said the mule, 'you were on the right track.'

They watched as the mule stood on its hind legs and started to shift form, gradually settling into a smooth bipedal shape not wholly unlike a mule's, but with smooth grey skin like a dolphin's. It had glowing red eyes and wore a distinctly fascistic black uniform.

'Christ on a bike!' Fitz exclaimed.

'So, you are time-travellers.'

26.'No,' lied Fitz, badly.

'Then could you explain how you know the name of a deity who is not yet born and a mode of transport that has yet to be invented?'

'Yeah, well, OK, we're time-travellers. We're one step ahead of you, and we're here to foil your plan.'

The alien gave a braying chuckle. 'You don't have a clue what I'm planning.'

'Are you going to trigger Mount Vesuvius?' Trix asked mischievously.

The creature frowned. 'By your human calendar it is 40 BC. The eruption of Vesuvius doesn't happen until 79 AD. Furthermore, we're over a hundred miles away from there.'

Trix smiled. 'Yeah, I knew that. He didn't, though.'

'd.a.m.n,' said Fitz. 'Now I owe her a fiver. So. . . what's your plan?'

The creature looked at them suspiciously, then clearly decided they weren't a threat. 'I am Thorgan of the Sulumians. Three hundred and seventeen thousand years from now, your human species will encroach on our domain in the eighth dimension. I have a sacred vow to deflect the course of human history to stop that incursion. And what I will do tonight will prevent the Treaty of Brundusium from ever being signed.' He gave a triumphant laugh.

'Eh?' Fitz replied, speaking for both himself and Trix.

'If the treaty isn't signed, Octavian will never divorce Scribonia!' the monster explained.

'Eh?'

The creature's eyes narrowed. 'So he won't marry Livia.'

Fitz shrugged. He looked over to Trix, who shrugged in turn.

Thorgan waved a hoof impatiently. 'Don't you see? If that happens, then Antonius won't be allotted the eastern imperial territories, and won't abandon Octavia for Cleopatra VII.'

'I've heard of Cleopatra,' Fitz said helpfully. 'I didn't realise there were seven of her, though.'

'Oh, come on none of this is exactly obscure,' the creature growled.

Trix was also puzzled. 'Brian Blessed!' she exclaimed finally.

'Eh?' Fitz repeated.

'He played Augustus in I, Claudius I, Claudius,' Trix told him.

'Eh? I thought he was on about Octavian?'

'They're the same person,' the creature said, clearly aggravated. 'After he wins the Battle of Actium, he renames himself Augustus.'

'That's a gross simplification of the history,' the Doctor said. He was standing behind the creature, and had changed back into his normal, velvet frock-coat.

'But exactly what I've come to expect from a Sulumian.'

'Doc-tor!' the creature snarled. 'I might have known.'

27.The Doctor moved to shake the monster's hoof. 'h.e.l.lo, Thorgan. I'd offer you a jelly baby but, you know: gelatine.' He glanced at the hoof then let go of it, a little embarra.s.sed. 'Gosh, it must be what? minus twelve hundred years since I saw you last.'

'Pisa,' Thorgan replied.

'There's no need to be like that, he was only saying ' Fitz chipped in.

The Doctor pointed at the mule-man. 'Thorgan was trying to kill Fibonacci before he wrote the Liber quadratorum Liber quadratorum. Imagine it, Trix: western culture without the ability to solve diophantine equations of the second degree.'

'Why, the whole face of human history would have been changed,' she dead-panned.

'Yes,' Thorgan cackled. 'And I vowed when you defeated me then, Doc-tor, that there would be a reckoning.'

He tugged a small silver box from his belt and held it in his hoof.

'Before I discreate you, Doc-tor, I will allow you to watch as I detonate the strontium grenade I planted in the peristyle of Octavian's villa.'