For five minutes I sat and listened to the systole and diastole of the large antique wall clock at the rear of the room. I had satisfied myself that the genuineness of the letters I had been able to examine was beyond dispute. Now, with no sign of either host returning, I turned my attention to the trolley of new material. The boxes were numbered with Roman numerals from VI onwards in a sequence that continued from the boxes I had already seen. With scarcely more thought than I would have given to helping myself to mashed potato at my own table, I took the next two boxes in the series and brought them across to the long table for perusal.

It was a moment that I would relive many times over and which would stitch itself to my consciousness like that handful of other moments – my belated first smoky French kiss, proposing to Leonora in the hills above Thrang, cradling Sarah’s purple and ventouse-distended head in the operating theatre – that seemed not just to make up the life I have lived, but to constitute the person I have become.

One Christmas, when I was nine and at a loose end around the house, I opened the door of the spare room next to the one I shared with my sister and spied the glistening handlebars of a brand-new bicycle: specifically, a silver Raleigh Chopper accessorised with rear-view mirrors and tassels fixed on the handgrips. Aware that I had violated some kind of taboo, I shut the door immediately, breathlessly, but with the after-image of the bicycle burned on my eyes in such detail that I felt I could have drawn it exactly. For my perennially impoverished and proudly middle-class presents, the Chopper was an uncharacteristically lavish and fashionable present. It surprised a desire in me so deeply felt that I wasn’t even aware of it until I opened the door. After that, I could not forget it. I questioned my mother all afternoon about my Christmas presents in the customary way, while she stonewalled me with riddles, which only enhanced my pleasure in the secret possession of my new knowledge. At bedtime, after brushing my teeth, I permitted myself one last peek at the bicycle, this time opening the door to the spare room wider. The bicycle had gone. Baffled, I waited fruitlessly for it to turn up on Christmas Day. The process of disillusionment was gradual, but it became painfully clear that the vanishing bicycle had in fact never existed; it was a kind of hallucination.

Now, opening the first folder from the first of the new boxes, I experienced the same shock I had on opening the door of the spare room and seeing the hallucinatory bicycle. Fortified with decades of adult disappointments, I waited for the elation to pass, for my blast of astonishment to resolve itself into something more trivial, but it only deepened. There in front of me was an autograph manuscript written in Johnson’s mature hand entitled ‘On Nightmares’.

‘Of the evils that afflict a distempered imagination, none chafe with such asperity as the conviction that the seat of reason is itself undone,’ it began, and continued on both sides of a dozen closely argued foolscap pages. The next box revealed another cache of undated letters, some of them close to inarticulacy in their heart-rending pleas for assistance. ‘These men – nay, pray, do what you can.’ And the next, a diary on scraps of paper that reminded me of something out of Gogol in its sense of disorder and persecution. This was a Johnson that everybody knew existed but revealed with an unprecedented clarity and in his own words: melancholic, existentially terrified, trying to beat away the shadows of his own unreason with logic and conviviality, and finally being left on his own to confront the darkness. The writing on the final page tapered away unfinished after the words ‘left with little hope, nay none’ with a smeared and dwindling line of ink as though the writer had collapsed over the piece of paper.

I gave an involuntary shudder. The two centuries between me and Johnson telescoped to nothing. It came to me forcibly, and for the first time that I could remember, that behind the famous words that had turned Johnson into a monument was a living man who smelled of sweat and woodsmoke, feared death, hunger and madness; whose literary afterlife could be no consolation for the suffering he had undergone in the poor and far-off country of the past.

In my rapture of discovery, I had left my magnifying glass to one side. I collected the glass from the chair where it lay and as I did so, for the first time, I was troubled by the stirring of doubts. Why had Malevin not shown Hunter the prizes of his collection? Why be silent about them? And where had they been for the last two hundred years? Was it really credible that a vein as well worked as this one could contain so much unknown, unimagined material? And it brought up something that had been bothering me from the start: the white gloves. Among library conservators, they are regarded as useless at best. The slight protection they offer is more than offset by the additional clumsiness they impose on the wearer. Malevin was bluffing. The gloves were a piece of theatre.

With a growing sense of anxiety, I scrutinised the papers under the white light of a halogen pocket torch that I had brought for the purpose. My stomach gave a lurch – the door pushed open; this time, no bicycle.

It’s a troublesome detail for would-be forgers to remember, but the good ones are usually aware of it: the bulk of paper in the eighteenth century was still what’s called laid. Laid is the paper of antiquity, it’s made using preindustrial processes that produce distinctive rib-marks in the surface. These kinds of markings were absent from most of the Johnson pages. They were smooth and blemish-free. It was unlikely, if not unthinkable, that Johnson would have had access to this quantity of wove – like a writer of the 1960s using a word processor.

Turning over more pages, I was sure now that I had let my hope trump my judgement. And yet the material still rang so true. The forgers had gone to elaborate lengths to fake the text, but there was an extraordinary incongruity between the sophistication of the material and the amateurishness of the physical forgery. Whoever had done it had forgotten to take into account the huge technological shifts that were occurring in Johnson’s lifetime. It appeared that the pages had been created by someone working from a job lot of old paper, some eighteenth-century, some early nineteenth-century. Now the ink suddenly looked suspect, and the ageing of the paper had an amateurish feel: tea bags? Candle smoke? There was an absence of dating on all except the most uncontroversial letters; the headings of the diary entries gave only the days of the week, as if the forger was unwilling to risk committing to dates in a verifiable year.

The room suddenly felt close and overheated. I clicked off my torch and stood up. I had a sense of dislocation, as though I had just seen the eyes in a portrait move. Phrases from the pages were still running through my head, yet now I knew the living, suffering man who had been speaking to me was no more than a trick of the light. That figure who had just seemed so close suddenly receded into a familiar image: quaint old periwig-wearing Johnson: ‘… should my testimony from this dark place spare another from a sojourn here.’ Amid all the other sensations was a feeling of loss. It reminded me of the quality I had always loved in Johnson: the solace of his fierce, suffering intelligence. Like a rare handful of characters in books, Johnson seems to project a vast empathy back out to the reader; he seems to know what it is like for the reader to live. Wholly pessimistic, he admits and grapples with the dark, unresolvable facts which everyone knows in their hearts to be true, but every age finds its own ways of avoiding: that life is a painful, chronic illness lightened by brief bouts of remission, that death comes stalking remorselessly down every corridor, that the extraordinary disjunctions of human suffering are tragicomic at best, and at worst entirely meaningless. And yet, his preparedness to hold onto these dismal truths performs a kind of alchemy. His moral courage is transformative, a guide and comfort, but also a kind of protection: Virgil leading Dante through Hell, Tinkerbell swallowing the poison meant for Peter, Christ at Golgotha. Like them, his example seems to say: You shall face these things, but you shall not face them alone.