Daniel Wilson looked full of trepidation as he and his wife, Abigail – known to the public at large as ‘the Museum Detectives’ – approached Marlborough House, the London residence of the Prince of Wales and his wife, Princess Alexandra of Denmark.

‘The last time I was here, the Prince had me thrown out.’

‘But not literally,’ Abigail pointed out.

‘He would have if I’d refused to leave,’ said Daniel. ‘I could tell by the look on his face. His man, Shanks, would have summoned a few more servants and I’d have been sitting on the pavement with my dignity in tatters. Yet today, here we are calling at the Prince’s invitation. I don’t understand it. What’s going on?’

‘The last time you came here it was to question him on his relationship with one of his mistresses,’ Abigail pointed out. ‘That is not the case this time.’

‘I’m still doubtful, about us being here,’ said Daniel. ‘He doesn’t like me.’

‘But he invited both of us,’ pointed out Abigail. And she took the brass bellpull beside the black oak door in her hand and gave it a tug.

At Scotland Yard, Chief Superintendent Armstrong slammed a big beefy fist down hard on the top of his desk.

‘The commissioner himself has ordered a blanket of silence over this matter!’ he snarled, enraged.

Inspector John Feather looked on in what he hoped appeared like sympathy. The fact was that over the years he’d seen the chief superintendent in similar rages when he’d been barred from what he saw as his right to publicity – in this case, the murder of a Yeoman Warder at the Tower of London.

‘A murder in royal premises!’ Armstrong raged. ‘The Tower of London, no less! There could be honours arising out of this case.’

‘We haven’t been barred from investigating the murder,’ Feather pointed out.

‘As good as!’ snorted Armstrong indignantly. ‘No involving the press. No talking to anyone. How are we supposed to catch the killer with our hands tied?’ He looked sharply at Feather. ‘This Dillon character. What’s he like?’

‘Viscount Harold Dillon, sir. The curator of the Tower of London. Quite a reserved sort of man. Very cautious in his manner and his speech. At least, that’s the impression I got when I met him.’

‘Has he got the ear of the royal family?’

‘Definitely, sir. The curator of the Tower is a royal appointee.’

Armstrong scowled. ‘We’ve got to get him to change his mind. We can’t solve this without talking to people. We need information.’

‘Yes, sir,’ agreed Feather, thinking to himself even as he said it: no chance.

‘You’ve got to find a way round this, Inspector,’ said Armstrong firmly. ‘We need to unmask this murderer. As I say, there could be honours at stake here.’

And I have a good idea who’ll be getting them if we do, thought Feather, and it won’t be me.

‘You’re investigating the murder of that Salvation Army officer in Whitechapel, aren’t you?’ asked Armstrong thoughtfully.

‘Yes, sir,’ said Feather. ‘Captain Merchant. He was found beaten to death not far from a pub, the Blind Beggar. By all accounts, the local publicans have no love for the Salvation Army; they accuse them of costing them money with their drive to stop people drinking.’

‘So, the publicans are the chief suspects?’

‘I wouldn’t say chief suspects, sir. There are rumours concerning the immigrant communities in the area, notably the Ashkenazi Jews and the Irish.’

‘No matter,’ said Armstrong dismissively. ‘The point is that Whitechapel is right next door to the Tower of London, so you’ll be over there, on site, so to speak. You can pop in and out without upsetting the curator, this bloke Dillon. Tell him you’re investigating the Salvation Army killing, and you’ve come to update him about the murdered Yeoman. See what he’s got.’

‘But if I say I’m there to update him, he’ll expect some progress,’ pointed out Feather doubtfully.

‘Make something up,’ said Armstrong. ‘The important thing is to be seen to be doing something, so that when a lead pops up at the Tower, it’ll be recalled that we – the Metropolitan Police – were the ones who were there. It was us who cracked the case.’

‘Yes, sir,’ said Feather.

‘Good,’ said Armstrong. ‘We have a plan.’

Daniel and Abigail perched on the sofa in the Prince of Wales’s library and listened attentively as he told them the reason for his summons. A Yeoman Warder had been murdered at the Tower of London and his body stuffed into the suit of armour that had once adorned the body of King Henry VIII, and was now on display in the White Tower as part of the famed Line of Kings.

‘Viscount Harold Dillon, the curator of the armouries at the Tower, feels it could be an act of violent sedition aimed at the royal family,’ said the Prince. ‘The concern is that it may be the tip of the iceberg, and there could be even more dangerous acts to follow. Assaults on members of the royal family themselves.’

Including you, thought Daniel.

‘I would like to commission you to conduct an investigation into this tragic affair and get to the bottom of it. Find out who is behind it. But …’ And as he stressed the word, he fixed them both with a determined look. ‘This must be done with no publicity of any sort. Such publicity could possibly inflame the situation, if it is republican anti-monarchists at work here, and encourage others to follow suit. It is important no word of this outrage leaks out. Not just to the press, but it must be kept from the public at all costs, by whatever means.’

‘We understand, Your Highness,’ said Abigail. ‘We assume the police have been informed. It is a legal requirement …’

‘Yes, yes,’ said the Prince impatiently. ‘They have. Viscount Dillon has been in touch with Scotland Yard. In fact, it was he who suggested we commission you to carry out his investigation, in parallel with the police. But, and I stress again, with no information going out to the press or the general public. That is paramount.’ He looked towards his secretary, Shanks, who sat at a nearby desk. ‘My secretary has prepared a letter to Harold Dillon authorising your investigation. He’ll give you that and you can make yourselves known to Dillon at the Tower. He’ll give you everything you need to know. And you’ll report to him.’

Shanks stood up and said, ‘If you’ll follow me to my office, Mr and Mrs Wilson, I’ll give you the letter, and at the same time fill you in on the background of the organisation of the Tower, which I feel may be of help.’

As Daniel and Abigail followed the Prince’s secretary along the corridor to his office, Daniel mouthed quizzically at Abigail, ‘The organisation of the Tower?’

Abigail nodded and put a discreet finger to her lips, followed by a wink to let him know that she would explain to him later if there was anything he didn’t understand.

Shanks’s office was small and spartan: a desk, his own chair behind it and two other chairs facing the desk. There were no paintings on the walls, no photographs on the desk, the shelves were filled with imposing reference books and registers of Europe’s aristocratic families.

Shanks gestured to the two empty chairs and they sat. He passed them the letter he had prepared authorising them to investigate the murder. ‘I have already sent a copy to Viscount Dillon by messenger,’ he told them. ‘Have either of you been to the Tower?’

‘Some years ago when I was a detective at Scotland Yard,’ said Daniel.

‘And I visited as part of my studies when I was at Cambridge,’ said Abigail.

Shanks nodded. ‘As I’m sure you know, the Tower is a royal palace. The building of the White Tower began shortly after the Norman invasion of 1066. I understand that you are known as the Museum Detectives. Effectively, the Tower is a museum, the oldest in Britain, but it is also a royal palace, and as such it comes under the authority of the Crown.

‘The most senior person in charge of the Tower is the constable. The constable is always chosen from the most senior ranks of those members of the military who have retired from active service. You may recall that earlier this century, the famed Duke of Wellington was appointed constable of the Tower. The current constable is General Sir Frederick Stephenson, a former commander-in-chief of the...