'Sorry we've missed her,' Sharp remarked.

'Your business is with me,' said Hall. 'There's nothing Marilyn can tell you.'

'There doesn't seem to be much you can tell us either.'

'True, I'm afraid. But…' Hall leaned back in his chair and spread his hands in a gesture hinting at conciliation. 'I accept your motives are honourable. I believe you're mistaken, though. Radd was responsible for my daughters' deaths. There's nothing any of us can do to bring them back. I've learned to accept that.' He fixed his gaze on Umber. 'Others must learn to accept their own loss. The idea that Sally was murdered…' He shook his head. 'It's simply not credible.'

'I believe it,' said Umber, with quiet emphasis.

'So do I,' said Sharp.

'I see.' Hall looked at each of them in turn. 'Well, let me tell you what I have in mind, then. I have business in the City tomorrow and the day after. I still sit on one or two boards. I can't get down to Marlborough until Tuesday night. That's really the soonest I can manage. It'll take time to talk all this through with Jane. And with Edmund, of course. But that's what we need to do. Discuss your concerns… calmly and rationally. Then…'

'Yes?' Sharp prompted. 'What then?'

'Report back to you, Mr Sharp. What else? If a joint discussion leads any of us to question the official view of the case, I can promise you our full support in reopening the inquiry.'

'You can?'

'Absolutely. I believe we already know the truth, dismal and tragic though it is. If I'm wrong, or if everyone else thinks I'm wrong…'

'All bets are off?' suggested Umber.

'Yes.' Hall smiled at him. But the smile did not reach his eyes. 'If you want to put it like that.'

Nothing was said during their ride down in the lift. For no logical reason, Umber felt unable to speak freely until he was off the premises. Sharp evidently felt much the same. They were in fact halfway between Kingsley House and the van before either of them broke the silence.

'He thinks he's got us where he wants us,' said Sharp.

'And has he?'

'This trip to Marlborough he's oh-so-reasonably agreed to take is just for show. He'll come back after a couple of days and tell us they're all singing from the same hymn-sheet: Radd guilty; Radd dead; end of story.'

'What can you do if that's the plan, George? You can't stop him going. Or dictate what he says to the Questreds when he gets there.'

'No. I can't.'

They reached the van and climbed in. Sharp started away promptly and did not speak again until they were turning into Berkeley Square.

'I don't have to sit around twiddling my thumbs while he plays his little game, Umber. And I don't intend to.'

'So what do you intend to do?'

'I'm going to Jersey.'

'You are?'

'No better time to size up Jeremy Hall than when his father isn't there to interfere.'

'You promised his mother you'd leave him out of it.'

'If I could. Well, I can't. Not any longer.'

'When do we go?'

'We don't. I do. I'm driving down to Portsmouth tonight. I've booked Molly and me on tomorrow morning's ferry. We sail at nine.'

'You've already booked the ferry?'

'Yup.'

'But… you couldn't have known… what Oliver Hall was going to say.'

'I could have cancelled if he'd proved more open-minded than I expected. Doubted he would, though. And I was right.'

'What am I supposed to do?'

'Go see Sally's therapist. Knuckle down to your research on Mrs Dallyroll. And cover my tracks if Hall or the Questreds get in touch before we're ready for them.'

'When'll that be?'

'No way to tell.' Sharp braked to a halt at the traffic lights on Piccadilly and glanced round at Umber. 'Let's just hope it's before they're ready for us.'

Irritated though he was at Sharp for booking his passage to Jersey without telling him, Umber could not deny that it made sense for one of them to go while Oliver Hall was out of the way. Umber was not free to leave London, so there was no choice: it had to be Sharp. His excuse for keeping Umber in the dark was that it had spared him from lying to Hall. Umber reckoned it was more likely Sharp feared he might give the game away. Since he had not been entirely open with Sharp about his dealings with Marilyn Hall, however, he was in no position to complain.

With Sharp aboard the ferry to Jersey, due to dock in the late afternoon, Umber spent Monday morning at the British Library. He ordered a further batch of books, which were certain to take several hours at least to be fetched, then worked his way through various entries in the Dictionary of National Biography in search of background information on what he now remembered referring to in his original researches as the Dayrolles Connection.

The known facts were tantalizingly meagre. Solomon Dayrolles was the nephew and heir of James Dayrolles, British Resident at The Hague for many years until his death in 1739. The date of Solomon Dayrolles's birth was unrecorded, but could hardly have been later than 1710 and was very possibly earlier, given that his first diplomatic appointment was as secretary to Lord Waldegrave, Ambassador to Vienna, a post Waldegrave held from 1727 to 1730. Dayrolles's uncle obtained the position for him through the influence of the young Lord Chesterfield, who was Solomon's godfather, despite the fact that he was born in 1694 and could therefore have been no more than a youth at the time of Dayrolles's birth.

Chesterfield was at this period winning his spurs as the great wit and cynic of Georgian political life. He had been a favourite of George II when the latter was still Prince of Wales, but offended the King after his accession by his attacks on the Prime Minister, Sir Robert Walpole. Chesterfield drifted into the opposition camp and the circles of the new Prince of Wales, George's hated son, Frederick.

Dayrolles meanwhile became a wealthy man on the death of his uncle and bought Henley Park, a country estate near Guildford, as his English residence. When the fall of Walpole restored Chesterfield's political fortunes and he was appointed Lord-Lieutenant of Ireland, Dayrolles accompanied him to Dublin as his secretary.

In 1751, Dayrolles married the eighteen-year-old Christabella Peterson, daughter of an Irish colonel. The couple had four children – a son and three daughters – and the marriage in no way affected his relations with Chesterfield, who had by then retired from active politics.

Chesterfield's old age was afflicted by tragedy – the sudden death of a beloved son – and illness. When he died, in March 1773, his godson-cum-friend was at his bedside. The Earl's last words were reported to be: 'Give Dayrolles a chair.'

Solomon Dayrolles died in March 1786, his widow Christabella in August 1791. Not until William Cramp produced his book Junius and his Works compared with the Character and Writings of the Earl of Chesterfield in 1851 did anyone suspect or suggest that Mrs Dayrolles might have written the letters of Junius at Chesterfield's dictation. Cramp's theory was generally ridiculed on account of the Earl's age and infirmity, the similarities between Mrs Dayrolles's handwriting and that of Junius dismissed as insignificant.

The handwriting. That was the nub of it. The similarities were too striking to be rejected without further study. Umber could remember thinking that when he had inspected some examples for himself, wildly improbable though Chesterfield's authorship of the Junius letters nevertheless seemed. He had learned what more he could about Christabella Dayrolles, though it had not been much and it had taken him nowhere. But where had he learned it from? There was no clue in the DNB entry for her husband.