The hands of Big Ben's clock moved on to the hour. The bell itself interrupted the Doctor's thoughts as it ushered in the afternoon. 'I hope you're sure about your theory,' said Benny.

'I'd hate to think we were standing here while Jason robs a Midland and Westminster Bank or something.'

'That doesn't exist yet,' the Doctor said distractedly. 'And I'm sure. My homing device tells me that the TARDIS is 154 nearby, in St James's Park. Jason is coming here, to contact those in power.'

He crossed his fingers and tried to shake the feeling that he'd missed something.

155.

17.

b.u.t.terfly People.

Lawrence Murdock knew nothing of time travel, but he knew a little about cause and effect. He could have said less on the subject of air currents, but he did know about b.u.t.terflies. One night in the pub, it had been explained to him: that the flapping of a b.u.t.terfly's wings could cause hurricanes, although he didn't really understand how. And Murdock knew from the TV that hurricanes killed people, sometimes in great numbers.

So, one day in early 2002, after reports of a particular tragedy on the evening news, he knew exactly who to blame for the carnage.

Lawrence Murdock knew how to use a gun. But he wasn't too proficient at aiming one.

In the summer of the previous year, Mark Waring thought he had a better way of saving humanity. He stood in Trafalgar Square, shouting to the public in hope of their buying his newspaper and being thus converted. Most weren't open-minded enough to seek enlightenment, so when two blond men in their early twenties approached, Mark saw them as a chance to double his day's takings.

One of the men extended a hand and Mark took it warily. The fellow was wearing what seemed like a school uniform. His more normal friend hung back as though embarra.s.sed. 'I'm Jason,' the schoolboy said. 'Why do you sell those?'

'Because I believe in what they say,' Mark answered, surprised that the question should have been put.

'Believe in what, exactly?'

'In the Marxist critique of contemporary society, of course. In the abolition of archaic cla.s.s boundaries and the redistribution 156 of the means of production. The purpose of this paper is to open people's eyes to our hegemonic domination by the ruling elite and to hasten the day of revolution.'

'Fab!' Jason said, clapping his hands enthusiastically. 'A friend of mine is planning a revolution today. Want to come?'

Mark regarded him suspiciously. 'You running a poster campaign?'

'No,' said Jason, in the same puzzled tone which Mark had just used. 'We're raising a rebel army to take over the country.'

Mark stared.

'I thought you wanted that.'

Mark turned to the other man for some clue; perhaps a wry grin to show that his friend was normally considered insane.

But he was staring steadfastly up at Nelson's Column.

'Well? Isn't this what you're waiting for?'

Mark looked at his newspapers, the headline SMASH THE STATE emblazoned across each of them. He turned back to Jason, unnerved by the fanatical light in his eyes.

'Don't be stupid!' he said. Then he walked off as fast as he could manage without running.

'You don't understand,' Jason called after him, voice catching. 'We're making history!'

Melanie Bush stood in her own future, outside the unchanged landmark of Buckingham Palace, and wondered how things could look so similar and yet feel so different. She was only peripherally aware that, to the two women beside her, the events of 2001 belonged to tales of distant ancestors.

The Doctor returned from his short but intense conversation with a tourist. 'You were right,' he told Benny, disgusted with himself, 'we were wasting our time. Jason came here.'

'Second rule of warfare,' said Benny. 'Don't overestimate your opponent either.'

'I should have learned that from the Vardans.'

'So what now?' asked Roz (itching to get into action, Mel thought contemptuously).

'I know something Jason doesn't. Benny, Roz, I want you to stay here. Keep an eye on the TARDIS, in case the barrier 157 falters, and guard the palace. He'll be back. Mel, you're with me. We need to be in Sheffield and I'm afraid the quickest route is by train.'

'Can't I go?' Benny asked. 'The north of England was really quaint at this time.' She dropped into an unconvincing hybrid Lancashire/Yorkshire accent. 'By 'eck la.s.s, tha's got a whippet in tha tripe bowl, bah gum.'

The Doctor frowned. 'What books have you been reading?'

Tina Matthews had been reading books about animal experimentation. That was why she wanted to change the world.

But she wasn't going to do it by listening to some jerk in short pants.

'Why not?' Jason pleaded, pursuing her along the road.

'Because you're nuts.'

'We can be nice to animals if that's what you want.' Jason tugged her elbow so that she dropped the leaflets she had been distributing. 'We can make you Princess with Responsibility for Wildlife, how does that sound?'

Tina swore as she knelt to gather the fallen papers. To her annoyance, he crouched beside her. 'What does it say on these?

"Stop Animal Experimentation"? We can do that.'

Abandoning the remaining leaflets, Tina got up to leave.

'Fine, then!' Jason said petulantly. 'Just don't blame me if we "accidentally" pa.s.s a law banning all makes of shampoo that haven't been dripped into cats' eyes!'

Tina whirled around and punched him on the nose. She was rather pleased to feel it snap.

'Cruncher' Simpson didn't think of himself as someone who could alter history. Faces, yes but history, no. But he was looking at twenty years this time, so with nothing to lose, he might as well throw in with anyone who could make things difficult for the pigs. Just for a laugh.

'Right lads,' Dr Who said. 'Now we're out of that depressing prison, let's make plans for our glorious take-over.'

'Shouldn't we get away from here first?' asked someone. Dr Who gestured towards the doorway of Charing Cross police 158 station. It had been bricked up, Cruncher saw. Not that that surprised him; no more, anyhow, than had this strange man's elaborate escape plan, which had involved sleeping draughts in the guards' coffee and a collapsible battering ram which the desk sergeant had failed to notice in the incoming prisoner's pocket. Ten minutes after Dr Who's arrival, the nine occupants of the police cells were back on the loose. Some more so than others.

'Chris! Key!' Dr Who shouted, alarmed as two thugs bolted.

'I haven't told you what to do yet. Come back!' He whirled as another erstwhile follower shrugged his shoulders and sloped off. 'Not you as well, Giles. Get back here, Tony. Where's Kyle? What happened to the two Neils?'

The gathering dissipated, Dr Who turning one way and another as he tried to reverse the exodus. 'If you're interested,'

he shouted forlornly after his would-be fighting force, 'I'll be at the Victoria Memorial at three.'

Cruncher clapped a hand on his shoulder. It was meant to be supportive, but it almost drove the fl.u.s.tered little man through the pavement. 'I'll be there, Doc!'

Dr Who smiled weakly, hiding his upset. 'I know, Cruncher.

Thank you.' Then he disappeared like the fading picture of an old TV set.

Cruncher shrugged and, unperturbed, headed for the nearest pub. He whistled airily.

Murdock came at Ace from behind. She cursed - forgetting your training, she reprimanded herself - as a bullet cracked by. She flung herself aside, rolled back up with her gun primed and aimed the weapon at his head. He fired again and Ace, alerted by the mad glint in his eye, barely managed to avoid this second shot.

He doesn't care if I kill him or not!

For a second, she considered it. She would have done, without compunction, if he had posed a threat. He didn't. The only threat here was time: in about a minute, the main door of the abandoned warehouse would be shouldered open and a posse of trigger-happy cops would storm in. Two would die.

They would kill Murdock in turn. Or at least, that's what the 159 papers said.

Ace rushed him with a feral cry. As she had expected, Murdock panicked. He wasn't a soldier. She disarmed him with a kick and brought him down hard. It was over in seconds.

'The police can find a nice soft room for you, sonny. Only let's get rid of the shooter first, eh? We don't want any accidents.'

To her disgust, her captive was sobbing. 'I only wanted to punish the b.u.t.terflies. We mustn't let them do it again.'

'Do what?' asked Ace as she emptied Murdock's automatic and flung it to the furthest corner. She realized that she didn't need an answer.

She remembered the news stories; the ones she had read nine months hence at Westminster Central Library. They had been pretty vague, but they had gone on about the timestream and the laws of cause and effect. That was what had attracted her to this place and time. The second on her list. The second event at which she had failed to find the Doctor.

Ace was familiar with the theory. A b.u.t.terfly flaps its wings; air currents shift; a year later, the effect might build up into a hurricane on the far side of the world. So Murdock had armed himself and taken on the job of stopping it. He had tried to kill all the b.u.t.terflies. He had managed to kill people instead.

The police had pursued him to the warehouse, where the forewarned Ace had been waiting to see if this unbalanced individual might have a connection with the man she was looking for. No such luck. But he had given her a few things to think about.

She had made a difference. The newspapers' mad gunman had been taken down after three accidental slayings, not five.

His life had been spared. And although, to Ace, this was all her future, just a few days ago, at the library, it had been history.

She tried not to think about it. She concentrated on the details of the third event on her print-out. She was going back to the end of 2001 this time.

As the police burst into the building, Ace coaxed the hopper into performing its next vanishing trick. Her last sight was of 160 Murdock, rolled into a foetal ball. He wouldn't even have had to destroy any b.u.t.terflies, Ace thought. A minor diversion in the path of the right one might have eradicated the future she had just come from.

Yet here she was, heading further back into the past, where she could be responsible for so much worse.

Christopher Cwej was worrying about the implications of his own actions. All the time he had been on Earth, two voices had been screaming in his head: one said he was doing the right thing, that it was only what he had tried on Detrios; the other told him to stop messing with his own past and get the h.e.l.l out of here. He was currently trying to hold both in abeyance whilst biting into an undercooked hamburger from a roadside stall and trying to detect any taste of ham.

Jason raced up the steps from the subway toilets, shaking.

'What happened?' Chris asked. He noticed that Jason's attempt to clean his nose had been unbelievably successful: there was now no sign that it had been broken.

'I think I talked to one of the enemy.'

'You weren't trying to recruit down there?'

'He said he liked my costume,' said Jason, short of breath. He clutched Chris's arm and hurried him away, checking over his shoulder. 'I didn't know what he meant at first, but he guessed I was looking for some men.'

'Oh.'

'And when he mentioned sorting out an old queen, I thought he had to be on our side.'

Chris changed the subject. 'Where are we going?'

Jason looked at his watch. 'Back to the Palace. We have a rendezvous with Dr Who at three o'clock.'

That was news to Chris. 'When did you arrange that?'

'I just did, all right?' Jason strode on ahead and Chris sighed, feeling his grasp of the situation crumbling.

Bernice Summerfield watched a young family feeding ducks in St James's Park. 'It's so peaceful. You wouldn't think time was about to unravel.'

161.

Roslyn Forrester scowled and hurled another stick at the TARDIS doors. Like the earlier ones, it exploded in flames. 'I can't get my head around this,' she said. 'We're almost a millennium into my past - if things had gone wrong here, I'd know. It's like when we went to the Great War: why risk our necks when we know things turn out okay?'

Benny shrugged and half laughed. 'Don't ask me. For all we know, we might already be part of this history. If so, we'd change things by doing nothing.'

suppose.'

'Or by stepping on the wrong blade of gra.s.s, shooting down the wrong person, kicking that c.o.ke can over there . . .'

'But what happens if we change things so that our times never exist?'

'Don't think I haven't wondered,' said Benny soberly. 'What if, each time I've visited the past, my history has subtly changed? If I changed with it, I'd never notice!' She shivered and wrested her thoughts from that image. 'Frightening, if you think about it. That's why I try not to. Come on, there's no point hanging around here, let's check Buck House again.'

As the two women left, Bernice kicked out deliberately at a mangled drinks can. It skipped and came to rest in the middle of the path. Four and a half hours later, the front Wheel of a young man's bike hit the displaced object. He suffered slight bruising, which his mother stayed up late fussing over. The young man's sister was conceived a month later than she might otherwise have been, and with different chromosomes. Her descendant never went on to join the Earth Peace Corps, so that a pivotal speech was drafted by someone altogether less eloquent. Earth was plunged into the Draconian war an hour early, and dozens more soldiers on both sides perished.

History shuddered and rewrote itself slightly. As paradoxes went, this one was minor and easily accommodated. Next time, the universe might not be so lucky.

Jason almost cried as he neared the Victoria Memorial and saw what the afternoon's efforts had wrought: just two recruits, a stocky man built like a shed and a tall girl with blue hair who 162 chewed gum and inspected her own fingernails. He recognized the latter as Jessie, one of his own efforts. She had been selling bootleg tapes on the street, describing her activities as 'a blow against the fixing of CD prices by collusive practices, innit?'

'Cor!' she exclaimed as Jason and Chris approached. 'Is this the 'ole rebel army then?'

'Size isn't important, Jessie,' Dr Who said, fairly dwarfed between his comrades-in-arms. He beckoned to Jason. 'I've brought out the battletank.'

'Oh, goody.' Jason brightened as he was led around the monument. He enjoyed watching Chris's eyes widen at the sight of the bulky metal dreadnought behind it, resplendent in canary yellow. A few onlookers had been attracted by the vehicle's incongruity, and one boy was bold enough to have climbed up onto its caterpillar tracks.