'You two did well tonight,' said Big Barry, coming over to join them.

Bolt nodded a thanks, thinking that it was typical of his boss to arrive and take charge of the scene long after the danger had passed and all the hard decisions had been made.

'We could have had a disaster on our hands,' continued Big Barry. 'If that bomb had gone off in a crowded area and it hadn't been raining…I don't even want to think about the implications.' He concluded by announcing that he was going to be recommending the two of them for bravery awards.

Mo grinned, and Bolt was pleased to see how happy he looked as he thanked their boss. Bolt thanked him too, but he was less effusive. In the end, an award didn't mean as much to him, although he knew his mother would be proud. He was more interested in getting an answer to the one question that had been bothering him through all this. 'Have we any idea what on earth this is all about, sir?' he asked.

Big Barry nodded. 'We're beginning to, yes, although we're still a long way from a definitive explanation. But you were right: the key's Sir Henry Portman.'

Bolt frowned. He knew that the photo in Dominic Moynihan's house couldn't have been a coincidence, but it was still a shock to think of Portman as a central player in this whole conspiracy. 'How come?' he asked. 'And what did Moynihan have to do with it?'

'Moynihan's a partner in Sir Henry's hedge fund, HPP. It's a very small and exclusive outfit, mainly dealing with wealthy private clients, and it's had a good reputation for making money over the years. But in the last year they've piled into some risky financial and banking stocks at exactly the wrong time, as well as some pretty iffy-looking mortgage-backed securities, and they've taken some big hits. Or, more to the point, their clients have.'

'One of whom's Paul Wise,' said Mo. 'He's been investing in them through one of his holding companies, hasn't he? We were looking at it just yesterday.'

Big Barry nodded. 'That's right. Ratten Holdings. They've got roughly thirty million with HPP. But twelve months ago it was a lot nearer fifty. Wise hasn't done at all well out of Sir Henry, but here's the strange thing. A lot of Sir Henry's clients have been taking their money out of the fund and putting it elsewhere because of its poor performance, but in the last three months Ratten Holdings have actually been putting more money in. In fact, they're now helping to keep Sir Henry in business.'

'But what's that got to do with all this?' asked Bolt, waving a hand towards the burning building. 'And what's it got to do with a lorry load of mustard gas?'

'Have you gents ever come across the term "short-selling"?'

'I've got a little bit of an idea,' answered Mo.

Bolt just shook his head. He'd never had much of an interest in finance.

'Basically, it's when someone sells a share they don't own, then buys it back at a later date, hopefully at a lower price.'

Bolt pulled a face. 'How the hell do you sell something you don't own?'

Big Barry shrugged. 'That's the financial industry for you,' he said, as if this explained it. 'I'm not sure how it works exactly but it seems the person rents the share from someone else, and then they just hand it back to him at an agreed time. Apparently, it's a very common practice among hedge funds. Anyway, the thing that's significant from our point of view is that HPP have been short-selling huge numbers of shares in British retail, leisure and insurance companies in recent weeks – hundreds of millions of pounds' worth. If the prices of these shares stay static or rise, then HPP are going to be in a lot of trouble, because they're already stretched financially. On the other hand, because of the size of their holdings, if the prices of all these retail, leisure and insurance companies were suddenly to fall significantly – and by significantly I mean ten, fifteen per cent – then they're looking at making the kind of profits that are going to reverse all their bad calls of the last twelve months. But it would take a catastrophe affecting the whole of the FTSE to cause that to happen.'

'My God,' said Mo, who looked genuinely gobsmacked. 'You think that they were going to blow that lorry load of mustard gas to cause some kind of stock market crash?'

'Well, given the individuals involved in this plot, it stands to reason. A big London-based terrorist attack would cause an automatic knee-jerk reaction on the stock market, and the shares whose prices would suffer most are those in the sectors that HPP were shorting.'

'This is Paul Wise's work,' said Bolt, who was finding it hard to believe himself. 'It has to be. I know some of these City boys don't have that much in the way of moral scruples, but there's no way someone like Sir Henry Portman would have had the contacts to get something like this up and running. But Wise… I wouldn't put anything past that bastard.'

'No, I agree,' said Big Barry. 'Someone high-level like Wise would have been running things, but Sir Henry was a willing partner, as was Dominic Moynihan. I believe Moynihan went out with Roy Brakspear's daughter for a while so he would have been the one who volunteered the information about her father's connections with dangerous gases. Then Wise would have used his criminal contacts to organize the actual logistics and hire Hook. Whether or not they intended to carry out a mass slaughter or give some sort of warning before the bomb was detonated we don't know, but knowing someone like Wise, they'd probably take the mass slaughter route, because that would have the bigger impact on the stocks.'

Mo shook his head slowly. 'What kind of people would do something like that?'

'Greedy ones. And I reckon Sir Henry and Dominic Moynihan were probably under a lot of pressure from Paul Wise. He's not the type to be very understanding about people losing millions of pounds of his money.'

'But I can't understand how they'd have got away with it,' said Bolt. 'Surely it would have been a huge coincidence them making a fortune like that on exactly the same day this bomb goes off?'

Big Barry shrugged. 'I'm no economist, old mate, but I heard once that one third of the world's money passes through the City of London every working day. If that's the case, then the money they would have made – fifty, sixty million – is just a drop in the ocean. So I doubt if it would have been picked up. An attack like that would almost certainly have been blamed on Islamic terrorists trying to disrupt the British economy, and with no witnesses left alive to say otherwise it would probably have been left at that. I doubt if anyone would have suspected a couple of UK-born City financiers, one of whom's a peer of the realm.'

An unpleasant thought struck Bolt. 'What can we prove against Wise?'

'I don't know,' admitted Big Barry, his expression not inspiring a great deal of optimism. 'Probably not a lot. Wise is an intelligent, surveillance-aware operator so he'll have been careful with his side of the planning, and I expect he left a lot of the actual logistics to Hook. With most of the conspirators dead, we're going to have to rely on Sir Henry testifying against him, and even then it's going to be difficult to build a case.'

'Have we brought Sir Henry in yet?'

'At the moment we haven't got enough evidence to charge him with anything, but we've got him under twenty-four-hour surveillance and his house has been bugged, so even if he farts we'll know about it.'

Bolt took a gulp of his coffee. 'Fair enough,' he said, even though he'd have been happier with Sir Henry Portman in a place where they could lean on him. Bolt was sure a high-living socialite who'd never known true pressure would crumble immediately.

At that moment, a shout went up among the assembled firefighters in front of the barn. The fire was pretty much out now and two horrifically charred bodies were being brought out. As Bolt watched, they were laid down on the gravel track, and two paramedics with body bags and the duty doctor came forward to complete the formalities.