I took up this paper and brought it nearer to the light and I was able to see that underneath the list and the instructions Pearce had penned several of the ornate question marks with which all his medical books are peppered, the symbol having an absolutely precise meaning to him, denoting always "Absence of Proof". I was about to lay the thing back in the book, when I noted that one of the ingredients Pearce had written down was buttercup-root and my memory told me that, although this fleshy bulb is seldom used these days in any medical preparation, it is and always has been included in every preventative men have ever devised against the plague germ, Pastuerella Pestis. And so I concluded – rightly, as I was about to see – that what I held in my hands was Pearce's own prophylactic against the pestilence.

That Pearce should have written the thing on waxed paper was perverse of him, for ink cannot properly adhere to it and so the writing will soon enough become invisible. Luckily, he had employed a very sharp quill (he was always extremely fussy about his pens and liked them to be thin) and so, when I held the paper in front of the light, the words were magically illuminated, having been scratched into the wax.

And so my little role in London 's great tragedy was revealed to me: I would become a pedlar of Pearce's prophylactic. I would merchandise hope.

The money remaining to me at the time of my arrival with Katharine in London was almost gone. We ate food bought by Frances Elizabeth and kept ourselves warm with coal paid for by her. In return, I helped her with her letters, correcting her spelling mistakes and teaching her some elegant phrasing. She seemed content with this arrangement, but I was not. The notion that all that stood between me and destitution were letters of complaint and supplication (written for poor people who could not truly afford the price of the words) made me uneasy and afraid. And so I vowed to myself I would make a living by selling Pearce's remedy even if, to do so, I would have to have as my customers the relatives of the dead or dying and so find myself entering those houses marked with red crosses and with the words "God Have Mercy."

I paid five guineas to an old apothecary I had known during my time at Ludgate. For this sum, he made up a large quantity of the medicine (it tasted quite pleasant, being infused in Malaga Wine) and sold me a gross of bottles. Hanging on the door of his shop, I noticed one of the strange, bird-like headdresses worn by doctors going into plague houses and I asked him whether I might borrow this from him. "You may keep it, Sir," he said, "for that doctor comes here no more, nor goes anywhere, nor has breath."

I took it down and put it on. It is made of leather and covers the head and face and shoulders entirely. In it are set two eye-pieces made of glass and a long beak through which one is able to breathe with difficulty, it being stuffed with sachets of potpourri, put there to protect the wearer from the corrupted air. With the headdress goes a leather mantle (not unlike the tabards we used to wear at Whittlesea) and thick leather gloves that reach to the elbows. Once inside these garments, I knew that whoever I have now become – whether Robert or Merivel or neither of these or a composite of the two – I had rendered myself completely unrecognisable, even to those who knew me well. I did not even look like a man, but like a duck, and I thought how fitting this was, for in peddling Pearce's prophylactic, the efficacy of which had never been proven, I was about to become no better than a quacksalver.

This realisation, though it dismayed me for a while, did not prevent me, as I walked back to Cheapside wearing my duck garb, from feeling an attack of laughter coming on when I caught sight of myself in the glass of a low window. Not even in my fur tabard nor in my three-masted barque had I ever looked so completely and utterly ridiculous. I laughed for so long and so uncontrollably that all who passed me, I could see from my little eye-holes, shunned me as one gone suddenly mad in the street.

I will describe to you how the winter passed.

In December, I went into a plague house and found a man newly dead from the disease and kneeling by him his wife, holding his dead hand and weeping. I asked her what could I do for her and she told me that no one on earth could help her, for the sneezing and shivering that are the first signs of plague she knew would come upon her within a short time. I was about to turn and leave when I heard myself say (in a voice I did not recognise as mine, muffled as it was by the duck snout): "If no one on earth can help you, why not let one John Pearce, who is under the earth, save you from death?" I then held out to her a bottle of medicine. She looked at it for a moment, but then shook her head and returned to her weeping. Despite my very dire need for money, it was beyond me to ask this brave, grief-stricken woman for the one shilling and threepence I usually charge for the remedy, so I nodded to her and went out, leaving the bottle on her table. Four or five weeks later, this person, who had been seeking me for several days, found me and put her arms round my neck and kissed my beak. She had taken the medicine and the symptoms of plague had never come and so she believed that I had saved her.

From this time, when word of this success began to spread, my business prospered. People arrived at Frances Elizabeth's house asking for the medicine, thus relieving me of the need to go into plague houses in search of customers. Frances Elizabeth banked up her fires and burnt herbs on them and would not go near the strangers at her door. And more and more she and Katharine stayed upstairs in the bedroom, Katharine in the bed (where from time to time I made love to her without telling her that it was a love born of loneliness and need, and not of desire) and Frances Elizabeth in a rocking chair. And the two of them dreamed of the child to come and sewed bonnets for him and knitted blankets for his little crib. Katharine would hitch up her skirts and put her hands round her belly that was grown so large and heavy, by the coming of the new year, she looked like a woman come to full term. And the mother would lay her head gently in the middle of the abdomen, where the navel protruded like a rosebud, and feel the kicking of the baby's limbs. They seemed to long so ardently for the birth that this longing took all their time, so that the letter-writing was neglected and even I, downstairs in the parlour with my bottles, was forgotten so that I had the illusion sometimes that I was free once more, as I had been as a student, and not tied to Katharine or to anyone in the world and that I couild walk out into Cheapside and start my life all over again.

I did not give the unborn baby a great deal of attention. I thought of him as belonging only to Katharine and to her mother and not to me, as if I had made them a present of him. They wanted their present to be male. They wanted the son who could rise to prosperity in the Office of Patents and they named him Anthony, after the dead father. And one evening, an astrologer was summoned. This astrologer frowned when he learned that I was born under the sign of Aquarius and whispered some words to himself that I did not catch. He predicted that the child would be large and healthy and that, in its infancy, it would learn "a very pretty way with laughter." He set the probable date of birth as the twenty-fifth of February and went away richer by ten shillings, leaving Katharine and Frances Elizabeth disappointed that he had not told them more.

"Of what use is laughter?" sighed Frances Elizabeth. "It has never brought anyone to riches."

My birthday came again. I made no mention of it and there was no rejoicing. I was sullen all day, remembering the foolish Dégeulasse and the false hopes of his wife and daughters. And towards nightfall I thought of Celia, of her grace and sweetness and of her singing.