Then there is Conan Doyle's life, which is also in fine fettle. He is too professional and too energetic ever to suffer from writer's block for more than a day or two. He identifies a story, researches and plans it, then writes it out. He is quite clear about the writer's responsibilities: they are firstly, to be intelligible, secondly, to be interesting, and thirdly, to be clever. He knows his own abilities, and he also knows that in the end the reader is king. That is why Mr Sherlock Holmes was brought back to life, allowed to have escaped the Reichenbach Falls thanks to a knowledge of esoteric Japanese wrestling holds and an ability to scramble up sheer rock faces. If the Americans insist on offering five thousand dollars for a mere half-dozen new stories – and in return only for American rights – then what can Dr Conan Doyle do except raise his hands in surrender and allow himself to be manacled to the consulting detective for the foreseeable future? And the fellow has brought other rewards: the University of Edinburgh has made him an Honorary Doctor of Letters. He may never be a big man like Kipling, but as he walked in parade through the city of his birth, he felt at ease in those academic robes; more so, he has to admit, than in the quaint garb of a Deputy Lieutenant of Surrey.

And then there is his fourth life, the one where he is neither Arthur, nor Sir Arthur, nor Dr Conan Doyle; the life in which name is irrelevant, as is wealth and rank and outward display and bodily carapace; the world of the spirit. The sense that he has been born for something else grows with each year. It is not easy; it will never be easy. It is not like signing up for one of the established religions. It is new, and dangerous, and utterly important. If you were to become a Hindoo, it would be regarded by society as an eccentricity rather than a derangement. But if you are prepared to open yourself to the world of Spiritism, then you must also be prepared to endure the jocosities and shallow paradoxes with which the Press misleads the public. Yet what are the scoffers and cynics and penny-a-liners when set beside Crookes and Myers and Lodge and Alfred Russel Wallace?

Science is leading the way, and will bring the scoffers low as it always does. For who would have believed in radio waves? Who would have believed in X-rays? Who would have believed in argon and helium and neon and xenon, all of which have been discovered in the last years? The invisible and the impalpable, which lie just below the surface of the real, just beneath the skin of things, are increasingly being made visible and palpable. The world and its purblind inhabitants are at last learning to see.

Take Crookes. What does Crookes say? 'It is incredible but it is true.' The man whose work in physics and chemistry is everywhere admired for its precision and truth. The man who discovered thallium, who spent years investigating the properties of rarefied gases and rare earths. Who better to pronounce on this equally rarefied world, this new territory inaccessible to duller minds and cabined spirits? It is incredible, but it is true.

And then Touie dies. It is thirteen years since she fell ill, nine since he met Jean. Now, in the springtime of the year 1906, she begins to lapse into mild delirium. Sir Douglas Powell is immediately in attendance; paler, balder, but still the courtliest messenger of death. This time, there is no chance of reprieve, and Arthur must prepare himself for what has been so long foretold. The vigil begins. Undershaw's clattering monorail is stilled, the rifle range placed out of bounds, the tennis net taken down for the season. Touie remains without pain, and easy in her mind, as the spring flowers in her room change to those of early summer. Gradually, she slips into longer periods of delirium. The tubercle has gone to her brain; there is partial paralysis of her left side and half her face. The Imitation of Christ lies unopened; Arthur is in constant attendance.

To the end, she recognizes him. She says, 'Bless you,' and 'Thank you, dear,' and when he raises her in the bed, she murmurs, 'That's the ticket.' As June turns to July, she is clearly dying. On the day itself, Arthur is at her side; Mary and Kingsley watch in awkward fear, half-embarrassed by their mother's paralysed face. In silence they wait. At three in the morning, Touie dies holding Arthur's hand. She is forty-nine, Arthur forty-seven. He is much in her room after her death; standing by her body, he tells himself that he has done his best. He also knows that this abandoned husk, laid out on the bed, is not all there remains of Touie. This white and waxen thing is just something she has left behind.

In the days that follow, Arthur feels, beneath the febrile exaltation of the bereaved, a solid sense of duty performed. Touie is buried as Lady Doyle beneath a marble cross at Grayshott. Messages of sympathy come from the great and the humble; from King and parlourmaid, from his fellow writers and his far-flung readers, from London clubs and imperial outposts. Arthur is at first touched and honoured by the condolences, and then, as they continue, increasingly disturbed. What exactly has he done to deserve such heartfelt sentiments, let alone the assumptions behind them?

These expressions of true feeling make him feel a hypocrite. Touie has been the gentlest companion a man could possibly have. He remembers showing her the military trophies on Clarence Esplanade; he sees her with a ship's biscuit between her lips at the Victualling Yard; he waltzes her round the kitchen table when heavily pregnant with Mary; he whisks her off to frozen Vienna; he tucks a blanket round her in Davos, and waves towards a recumbent figure on an Egyptian hotel verandah before launching a golf ball across the sands towards the nearest Pyramid. He remembers her smile, and her goodness; but he also remembers that it is years since he could put his hand upon his heart and swear that he loved her. Not just since Jean came along, but before that too. He has loved her as best a man can, given that he did not love her.

He knows that he should spend the next days and weeks with his children, because that is what a grieving parent does. Kingsley is thirteen and Mary seventeen: ages which now surprise him. Part of him has frozen time at the day and the year when he met Jean – the day his heart was utterly brought to life, and also placed in a state of suspended animation. He must accustom himself to the notion that his children will soon be adults.

If he needs any confirmation of this, Mary soon provides it. Over tea one afternoon a few days after the funeral, she says to him, in an alarmingly grown-up voice, 'Father, when Mother was dying, she said that you would remarry.'

Arthur almost chokes on his cake. He feels his colour rising, his chest tightening; perhaps this is the seizure he has been half-expecting. 'Did she, by God?' Touie certainly never mentioned the subject to him.

'Yes. No, not exactly. What she said was…' and Mary pauses while her father feels cacophony in his head, turmoil in his guts '… what she said was that I was not to be shocked if you were to remarry, because that is what she would want for you.'

Arthur does not know what to think. Has some trap been laid for him, or does no trap exist? Did Touie after all suspect? Did she confide in their daughter? Was it a general remark, or a specific one? He has lived with so much damned uncertainty over the last nine years that he doubts he can bear any more.

'And did she…' Arthur tries to sound jocular, while realizing that this is not the right tone – but then there is no right tone – 'And did she have any particular candidate in mind?'

'Father!' Mary is evidently shocked by the very notion, as well as by his tone.

The conversation passes to safer ground. But it stays with Arthur through the following days, as he takes flowers to Touie's grave, as he stands, distracted, in her empty room, as he avoids his desk, and finds he cannot face the letters of condolence, the letters of true feeling, which continue to arrive. He has spent nine years protecting Touie from the knowledge of Jean's existence; nine years trying never to give her a moment's unhappiness. But perhaps these two desires are – always were – incompatible. He readily admits that women are not his area of expertise. Does a woman know when you are in love with her? He thinks so, he believes so, he knows so, because that is what Jean recognized, in that sunlit garden, even before he himself was aware of it. And if so, then does a woman know when you are no longer in love with her? And does a woman also know when you are in love with someone else? Nine years ago he devised an elaborate plot to protect Touie, involving all those around her; but perhaps in the end it was only a scheme to protect himself and Jean. Perhaps it was entirely selfish, and Touie saw through its fraudulence; perhaps she knew all along. Mary cannot suspect the full burden of Touie's message about remarrying, but it gets through to Arthur now. Maybe she knew from the start, watched Arthur's squalid rearrangements of the truth from her sickbed, understood and smiled at every mean little lie her husband told her, imagined him downstairs busy at the adulterer's telephone. She would have felt helpless to protest, because she could no longer be a wife to him in the fullest sense. And what if – now his suspicions become darker still – what if she knew about Jean's importance from the start, and went on guessing? What if she found herself obliged to welcome Jean to Undershaw while imagining her Arthur's mistress?