We were nearing St Paul 's. I did not know how long the praying of these Flagellant people might last once they went inside the church, and so, mindful of my errand of the ink, I decided to approach them straight away and ask them to spare me a few minutes before they began their prayers.

Coming up to the group from behind, I noticed how, on the shoulders of two of them, there was a rash of small wounds, as if the skin had been pricked and burst, and that some of these were infected and running with pus. And so I began my conversation with them by saying (quite loudly, so that they would hear me over their wailing): "Let me tell you good people that I am a physician and if ever the pain of your wounds becomes greater than you intend… I could give you a balm for it, to make it less…"

They turned and all stared at me and I saw that their faces were smeared with a white paste they had put on to make themselves resemble skeletons. I understood then that it was their intention to frighten people away and, indeed, they appeared somewhat affronted that I had had the temerity to approach them.

"Our pain," said one of them curtly, "is never greater than we intend, nor is it less, and as for you, the physicians, why do you not punish yourselves?"

I replied that, in my own case, fate had punished me so well that I felt relieved of all necessity to do so and I laughed at my own flippancy, hoping perhaps to elicit some answering smile from the Flagellants, but getting none. So I moved quickly to my question. "Look about you," one of them said in answer, "and you will see, not London, not a city with which you were once familiar; you will see a place come to chaos. The man who must live within chaos will go mad very soon. But we shall not. For we do not see it nor hear it nor smell it. All that we feel, all that we know is our own pain."

I thanked them and left them to go on their way. I walked very slowly towards Cloak Lane, where I hoped to purchase the ink for Frances Elizabeth, provided my ink-man had not died of the plague while I had been away. As I walked, I pondered the words and actions of the Flagellants and asked myself how best I should live in this "place come to chaos" in order to keep such sanity as remained to me. And I decided not to turn my face.away from the sufferings of the city but to try to measure them and define them. I would walk about. I would try to paint a picture of the plague (no, not on canvas!), a picture in my mind of where it was and how it traveled and all the things men and women had devised to make it leave them. And so I formulated a kind of plan with which to confront the slowness and sadness of time. And this making of a plan cheered me.

As Katharine grew heavier with her child, she became very heavy with sleep. And the mother, too, as if in sympathy with her daughter, would nod and doze over her letters in the room kept hot by the fire, and so I would creep out of the house, leaving the two of them to their dreaming, Katharine's white arm trailing down towards the floor, the mother's head fallen onto the table.

They did not ask or seem to care where I was going. They knew I would return, for Katharine had made me swear upon the green slippers never to practise or perfect any Leaving Step. And so I embarked on my "picture" of London, going sometimes north from Cheapside, but most often south towards the river and my old haunts, knowing that in these places every change would be visible to me and all of what I saw I would understand.

I did not visit Rosie. In her very street were two houses marked with the words "God Have Mercy On Us" and nesting near to the water at Southwark I saw a great quantity of rats. Yet you could not say that Rosie Pierpoint was in greater danger of the plague than any in Lambeth or Spitalfields or Shoreditch, because the disease did not seem to follow a traceable path along the ground, but rather to come out of the air, like seeds carried on the wind and falling here and there at random.

There was some noise, still, upon the river, but less than there once was, many of the fops and gallants and their women having fled into the countryside taking all their shrieking with them. I was told that some of the bargemen were starving, for lack of trade, and so made it my habit to have myself rowed some way on the water every afternoon. And for this act of charity, I was rewarded with the gossip of the river and heard how, to add to the melancholy of London, hundreds of poor seamen, sent away from their ships unpaid, had come in to the capital to beg money from the Navy office, and how these, because they had no shelter and no fire, were easy victims of the pestilence "but have no place to die in, Sir, but the street and so do make some disgusting deaths in the gutter."

"Why are they not paid?" I asked the bargemen and all of them gave me the same answer, which was that there was no money, the King "being very wasteful of what the Parliament gives him, as if he believes he has only to feed them false promises and they will shit gold on and on." And so I thought of what the King had said about his "honey-moon" being over. I had not believed him, but I saw now that he was right: he was loved less than before. Except by me.

It was only after several weeks of my wanderings about London that something of great importance became clear to me: I was not merely trying to understand the calamity of the city, I was trying to find for myself some role within it. So I began to ask the bargemen and the vendors of eel pies and the ink-man in Cloak Lane and everybody who would talk to me, "What can I, a trained physician, best do at this time?" But I got no satisfactory answers. Some people spat at me, as if the word "physician" had rendered me utterly repellent to them. Others advised me to go home and close my door and burn cleansing herbs over my fire and wait for time to pass. Others again began taking off their clothes and exhorting me to examine their bodies for spots and swellings. No one told me how I could become useful. And I think I would have continued aimlessly walking, noting, talking and watching if I had not one night woken up beside Katharine and heard in the room and in my mind a silence so profound that it is beyond words to describe because I cannot liken it to anything on the earth. I lay in it and looked at the dark and waited to understand what it was. And after a few minutes (minutes I could not hear passing but only sensed them pass) I knew that what had returned to me was the Silence of Pearce.

It is a thing that I find very difficult to endure, so lonely does it make me feel. I could not continue to lie motionless within it, so I rose and went down to the parlour and sat by the embers of the fire and waited for morning. But it was winter by this time, and I knew that this wait would be long, so to occupy the time I went upstairs again and fetched from under the bed (where I kept my few books and letters in one of the Whittlesea floursacks) the copy of William Harvey's De Generatione Animalium that had been given to me on my day of departure by Ambrose. It was Pearce's copy. It had been read so many times by him that the pages had become as thin and fragile as the petals of flowers, so frail in fact that one hardly dared to turn them. The black leather in which the book was bound was stained and torn, but it had been held for so long against Pearce's heart that it smelled faintly of him and, on putting it into my hands, Ambrose had said, "This was a part of John and is a replacement for the ladle."

I laid the book on my knee and opened it, turning the pages carefully, one by one. Certain of Harvey 's Latin sentences had been underlined by Pearce and on almost every page there were annotations in Pearce's minuscule writing. In the heart of the book, seemingly put there long ago and forgotten, I discovered two pressed primroses and laid into the pages with them was a piece of waxed paper upon which the Greek word meaning "prophylactic" had been written. Beneath this was a list – in English as far as I could decipher it – of ingredients, followed by short instructions as to how they should be mixed.