This had never occurred to Luis, who rarely had cause to go far underground. He muttered defiantly, ‘Well, I didn’t know we were prepping for a test.’

At last they came to a better fitted chamber, with decent gaslights casting a clean glow over a smart but not ostentatious suite of furniture, a thick carpet, walls lined with bookshelves, and ceiling-to-floor mirrors that Luis guessed were intended to give an impression of space in this enclosed room. Open doors led to adjoining rooms. It was like the reception room of an unpretentious family of reasonable but not overwhelming means, Luis thought, based on his own limited experience of such places.

A small group of men were already in the room, mostly dark-suited, leaning on the mantel or sitting at their ease. The Waltzers stood in a rather self-conscious huddle on the carpet, but Oswald boldly struck a pose.

At length a major-domo type smoothly effected introductions, and as he did so Luis felt his own amazement grow. A man in his middle thirties, perhaps, stern, sharp-looking, in an anonymous suit, was named only as ‘Mr Radcliffe’. Two burly butlerish fellows at the back of the room were not introduced, and Luis concluded they were either special constables or military men out of uniform, no doubt backed up by others elsewhere. But a grumpy-looking gentleman in his fifties who remained seated, rather rudely, with a sparse carapace of hair and bone-white mutton-chop whiskers, turned out to be none other than Lord John Russell, the Prime Minister.

And a handsome, well-built chap leaning casually against the mantel, in a crisp morning suit but with an intimidating set of whiskers of his own, was Albert, the Royal Consort.

The Great Elusivo had played some tough houses, but he felt utterly bewildered before this audience, even though Albert quickly insisted that no formality of behaviour was necessary. And he wondered whether somebody in the royal circle or the government – perhaps this sternly watchful fellow Radcliffe – had thought through the consequences if any of the Waltzers had intended any harm to this royal personage. For, if they turned out to be dangerous, where better for such a meeting to take place than underground, from where, as Burdon had pointed out, none of them could Waltz away?

‘Dr Hackett,’ said the Prince. ‘It is very good to see you again.’ His accent was a crisp, heavy German.

Hackett answered proudly, ‘Thank you, sir. Gentlemen, His Royal Highness has taken a keen interest in our – ah – novel proposal of service from the beginning. As I have described before, sir, the talent we share is just as I demonstrated to your assistant Mr Radcliffe that evening in Windsor Great Park some weeks ago. And now, during the Chartist Demonstration at Kennington, I hope we have shown its efficacy in practice. We – move aside. I could not tell you how we do it, any more, I dare say, than a newborn babe could explain to you how he took his first pace. We find ourselves in another place, a sort of forest. I’ve no idea what the significance of that is, which part of the world it might be – if it’s our world at all. Perhaps we should send a naturalist to explore. Call for Mr Darwin!’

The Prince was gracious enough to laugh at this.

But the dour Radcliffe seemed to lack a sense of humour. ‘Your flash doesn’t impress. It is your utility in this world which is of interest to us, Dr Hackett.’

Flash – a bit of London street slang. The word jarred in this context, taking Luis by surprise. Perhaps there was more to this Radcliffe than there seemed – and, yes, an element of threat.

But Hackett was unperturbed. He said smoothly, ‘Of course, of course. And you understand the principle of that utility, just as I demonstrated in the Great Park. I Waltz into the forest.’ He took a pace to the left to demonstrate. ‘Then I walk through that forest.’ He took one pace forward, two.

As he approached Prince Albert, Luis saw how the butler types at the back of the room, and indeed Radcliffe, all stiffened, fully alert.

‘And then I come back.’ A pace to the right. ‘Poof! I have disappeared, and reappeared out of thin air, somewhere else. Like a cheap stage illusion,’ and he couldn’t resist a wink at Luis. ‘It is not just that I have been unobserved, you see. It is that I have, umm, bypassed any obstacle in this world – a wall, a line of troops, the hull of a bank strongroom. That is the secret of our utility to you.’

‘You mention a bank,’ said the Prince. ‘It does appear that this faculty of yours would be of uncommon value to a thief.’

‘True enough, sir. And maybe there are fellows out there in the world who would use this talent for such nefarious ends.’

Luis whispered to Fraser, ‘He says it without blushing, despite what he’s told us of his own rakish past!’

‘There are, naturally, few authenticated accounts of the more honourable exploits of Waltzers like us in the past. I can only tell you of family traditions, passed down from father to son, though I do have some scraps of documentation in certain cases …’

Fraser whispered, ‘And here comes Hereward the Wake again.’

But Hackett didn’t go so far back this time. Instead he spoke of the Armada. ‘Of course the court of Queen Elizabeth was replete with spies and agents. But my own distant ancestor did more than most to penetrate Philip’s admiralty and return with plans of the invasion fleet. Elizabeth never knew of it, it’s said, but he got his hand shaken by Sir Francis Drake. A few tens of years later another ancestor helped destabilize Cromwell and his Roundheads, for their godlessness made them prone to superstition, and they were bedazzled by a bit of fake haunting. Dash on another hundred years and a distant uncle was popping in and out of the camp of the Jacobite Pretender as he marched into England during the revolt of ’45, getting up to all sorts of mischief. And I’ll admit to a bit of work on the other side, when one of my great-great-aunts, of a colonial family, spied on Lord Cornwallis during the American war.’

He sounded to Luis like a patterer in the New Cut, and perhaps he was overdoing it. But he seemed to be holding Albert’s attention.

‘At any rate here we are, sir, at the beginning of your own long reign, ready to put our talents at your service. Call us your Knights, sir. The Knights of Discorporea!’

That seemed to amuse Albert. ‘Though I own there was no such goddess.’

‘Well, there damn well should have been!’

Albert nodded. ‘I have consulted with Her Majesty on this. We are agreed that it is best that such a – unique – resource as you and your men comprise should be kept secret, within as tight a circle as possible.’ He glanced at Russell, who glared back; the Prime Minister hadn’t said a word, and was evidently resentful at wasting his time on a whim of the Prince, as Luis guessed he saw it. ‘Of course,’ Albert went on, ‘your operations must be carefully controlled at all times.’ And here he looked to Radcliffe. ‘It does seem to me in fact that your greatest value may be in countering similar agencies operating for our rivals and enemies – for I don’t imagine you would argue that such a talent as yours is an exclusively English trait, Dr Hackett?’

‘Indeed not, sir, and you are wise to point that out.’

‘But, yes, we do accept your offer of service. How could we refuse?’ He paced, grave, thoughtful. ‘I have a dream, you know, of unity in Europe and beyond – a brotherhood between the great powers, yes, even between Britain and Prussia. But in this year of petty rebellions many of my own relatives have been ousted from their thrones.’ He glared at the Prime Minister. ‘There are debates at the highest level of government about the destabilizing effects of Palmerston’s foreign policy, but for me this also causes personal distress – distress for my family, and for my ideals. I believe, you see, that we must all, men of honour, serve as best we can. I had it in one of my addresses – perhaps you remember it, Russell? “I conceive it to be the duty of every educated person closely to watch and study the time in which he lives, and, as far as he is able—”’