I go downstairs and I hear myself tell the musicians, who have just arrived, that my party has been cancelled. I give them money and bid them go home. I then call Will and instruct him to ride to de Gourlay's house and tell the family that I am ill and that there will be no musical evening.

At this moment, Celia descends the stairs. She is wearing a dress of dove grey taffeta, its bodice laced with apricot ribbons. In her hair, newly curled into ringlets, are more ribbons of this same bewitching colour.

I cannot move. Down she comes, down towards me, and for once she is smiling and I know that this smile is for me, and I feel the beauty of it, right to my bowel. And so at last, at the end of this most troubling day on which I have been told that my life is edging towards a great fall, I admit to myself what I have known since the night of the Bathurst's party, that I have done the one thing of which the King believed me to be incapable: I have fallen in love with my wife.

Chapter Twelve. A Drowning

I am ashamed to set down what happened on the evening of my birthday, yet I will try to do so, in the hope that the act of writing will assuage my guilt somewhat and allow me the rest that has eluded me for two nights.

I was not hungry and the thought of the elaborate meal I had had prepared for Dégeulasse and his family disgusted me. All I wanted was to be alone with Celia.

Taking her hand (I tried to make this gesture a gentle and affectionate one, but I fear it was rough and peremptory) I said: "Celia. It is a clear night. Come with me to the roof and we shall look at the stars through my telescope and try to read our futures."

Celia protested that she would feel cold upon the roof and that our absence would be discourteous to my guests.

"There are no guests," I said. "No one is coming."

At this moment, Finn appeared in the hall, dressed in his scarlet and gold attire and his blond wig. He looked reproachfully at my hand gripping Celia's wrist. "You may take off your silly garb, Robin," I said acidly. "There is to be no evening."

(My jealousy of Finn is like a tumour on my liver. It spreads and I grow jaundiced and sick.)

So I climb up to my roof, pulling Celia after me. We step out onto the freezing leads. I stare up at the sky and there is the crowded Cosmos, infinite and beyond measure. Of all the conflicting rules that govern its existence, I am ignorant, even, of the first one, or so I discover.

Celis is shivering. I take off my coat (a black camlet thing, frogged with gold braid) and put it round her shoulders.

I put my eye to the telescope. As I scan the sky, I see, at first, only the meaningless dust of the heavens. Then I notice that the planet Jupiter, with its little girdle of moons, is very bright tonight. "Ah," I say, posing as a man who knows his way about the planets and the stars, "voilà Jupiter. Uncommonly bright. Excellent. A good portent. Jupiter being of course the reigning planet of all earthly Kings. So we are smiled upon from on high."

I guide Celia to the telescope. Despite the little warmth afforded by my coat, she is still trembling. I am reminded of the fear of the afternoon. The knowledge that Celia is afraid dismays me. I must soothe and quieten her. So I put my arms around her. She cannot pull away from me, for we are on the very precipice of the roof. "No, Merivel!" she cries out. But I cannot let her go. I cannot. I have not the will. I turn her towards me. She tugs her head away from me, just as Wise Nell tried to do so that I would not touch her teat. It is not my hand that reaches for Celia's neck, but my lips. On the very place where a witch may suckle her creature, I begin to kiss her. She struggles and cries out again, but I do not let go. And now I am no longer satisfied with the smooth flesh of the neck. I want her mouth. Using all my strength, I bring her head towards mine. I feel her breasts against my chest. My head is throbbing and my breath coming in short gasps. And I force upon her a lover's kiss.

Not for one moment does she yield, but struggles every instant to be free of me. I am hot now. As heated as a boy with wanting. Celia arches her back, frees her mouth from mine. In place of the lost kiss I smother her with words. I beg her to think no more about the King. "If he is not weary of you now, then in one year he will be. For have I not said it, he is mercury and cannot be held or kept. He will never give you the child you want, Celia. Never! But I could give you a child. Have my son! For I am your husband and all I ask of you is that you allow me to love you!"

And then she spat at me. She spat in my eyes, blinding me for a brief moment – long enough for me to slacken my grip and for her to stumble towards the window through which we had climbed, letting my coat fall from her shoulders. When I turned, she was clambering in and screaming, screaming for Sophia, the odious Farthingale.

I could have followed and caught her. I could have thrown her down on the attic floor.

I did not. I wiped her spittle from my eyes. I damned God and damned my parents for my foul nature. I cursed a world in which I had no one to love me but whores and courtesans. I kicked violently at the base of the telescope, thus cruelly bruising my toe.

Though shivering very grievously, I stayed upon the roof for a while, as if trying to fill my being with the icy night.

I do not know what time it was when I crept back inside the house. I closed the window. As I walked through the attic towards the stairs, I noticed a sweet but sickly smell which I knew to be familiar, yet I could not remember what it was.

I have slept a little. How many days have passed now since my birthday, I do not know. I seem to have lost hold of time.

I had a diabolical dream. Finn, naked but for a green singlet, made love to my wife up against a wall. I killed him. I shot him in the buttocks with twenty-nine arrows.

When I woke, I remembered where it had come from, that sweetish smell in the attic: it is the smell of Finn's wig. And so I conclude, he is a spy. Either of his own making, or sent here by the King. There is no doubt he saw all that passed upon the roof, and will report it to Whitehall, thus causing me to appear, not merely silly, but grievously misguided – an opinion of myself I find it most easy to share.

And I enquire of this sottish Merivel: "How have you arrived at this state of affairs? (You, who thought yourself to be utterly indifferent to quiet Celia, liking only women of vulgar plumage.) Is vanity the key? On your wedding night, the King lay with your wife, while you plunged to oblivion with a village jade; have you, since that night, aspired to replace the Monarch in Celia's heart?"

It is beyond my comprehension. Love has entered me like a disease, so stealthily I have not seen its approach nor heard its footsteps. My mind recognises the folly of it and yet I still boil and burn with it, precisely as with a fever.

To whom or what shall I turn in order to be cured? From his damp habitation, I hear Pearce make a Pearcean reply: he does not pause or hesitate before instructing, "To yourself, Merivel."

I am composing, upon paper, an apology to Celia. I have set down that "certain events occurring upon my birthday so troubled me that my brain was prey to a sudden spasm of madness, causing me thus to force myself upon you so odiously", but seem unable to proceed with my letter further than this, causing me to wonder whether the lies and fictions underlying all human discourse may be a primal cause of the impenetrable silence we hear within our own skulls.

I sit and stare at my piece of vellum. I brush my lip with my quill. My anus aches with a fidgety tiredness, likewise my right leg. My hand upon the paper is chill. I cannot lie to myself about how ill I feel. I conceive the idea that I may be dying and feel cheered by it, releasing me as it does from the burden of declaring myself to be mad. My thoughts, as you will have discerned by now, are in a boiling muddle. To add to my discomfort, I have found lice in my hogs' bristles, which vermin plague me with an unendurable itching. I have instructed Will Gates to prepare a head bath of vinegar and guaiacum, a remedy I patented myself while at Cambridge and for which my fellow students, unwashed and lousy as they were, came eventually to thank me.